AFAIK, there is no MIDI command for previous/next in the Live Set. (Even if there were, since it wouldn't be a standard MIDI Program Change command, the OneControl GeckoMKII wouldn't help anyway.)

I believe the MODX does have its own footswitch function for this, though,

ETA: Balance of reply removed, as it was inconsistent with Bad Mister's better information below.

AFAIK, there is no MIDI command for previous/next in the Live Set. (Even if there were, since it wouldn't be a standard MIDI Program Change command, the OneControl GeckoMKII wouldn't help anyway.)

Live Set locations are not programs (Performances), they are pointers to programs (Performances) that exist elsewhere. If a certain Performance is invoked by Program Change 1, it will always be invoked by Program Change 1, regardless of which (if any) of the 16 slots of a Live Set you decide to place it in. So from a MIDI perspective, your 16 Live Set sounds are not going to be MIDI Programs 1 through 16 (unless you happen to put Performances 1 through 16 there), they are going to be 16 numbers unrelated to their location in the Live Set. So advancing through 16 incrementally consecutive MIDI Program Change commands can't work to navigate through a Live Set. I believe the MODX does have its own footswitch function for this, though,

I did realize this for the most part. I wish there was a simple solution for this, other than adding another footswitch to my pedalboard. Likely two, if I want to be able to go forwards and backwards, though I'm not sure if that's even an option.

This is probably something like Camelot could accomplish if it interfaced with bluetooth page turner hardware and internally kept track of which slot you're on. It would ignore when you manually change Performances using the keyboard. When you start Camelot - it could send the MSB/LSB/PC combo for Live Set slot 1 - then send the right next MSB/LSB/PC combo when you click the pedal "next" and the right previous when you click the pedal's "previous" button. Not perfect (because there's not a way to query for current Live Set slot) - but probably manageable. Oh - and I don't think it exists.

You need a device that is a bit more sophisticated than the one you describe (seems to be designed for a guitar player that has simple Program Change requirements) looks like its great for advancing through a couple of setups. The MODX uses both Bank Select and Program Change if you wish to address it via MIDI ... The shear number of Programs requires a bit more sophistication.

A simple Foot Switch (costing a fraction of the device you describe) will advance you through your MODX “LIVE SET”.
Plug a Yamaha FC5 Foot Switch into the MODX Assignable Foot Switch jack
Press [UTILITY] > touch “Settings” > “MIDI I/O” > Set “FS Assign” = Live Set+

Now, whenever you step on the FC5 (no matter what screen you are on) the pedal will advance you through the active Live Set.
The “active” Live Set is the last one you have selected. Live Sets can exist in User, and in each ROM Library. The FS will advance you through the most recently activated Live Set.

If you absolutely positively have to do it via MIDI with your feet...
If doing this via MIDI is a requirement, the currently active Live Set slot can be navigated by using Bank Select and Program Change commands... this might require a device costing several times more than the device you describe. Sophisticated pedal boards like the Yamaha MFC10 is a highly programmable MIDI Foot Controller - but can handle the required messages.
MSB 62 / LSB 0 / PC 0-15 would navigate Page 1 of the currently active Live Set.
MSB 62 / LSB 1 / PC 0-15 would navigate Page 2 of the currently active Live Set
And so on... there are 16 Pages... per Bank.
There are 8 Banks.

The simplest (least expensive way) is to reach up and press the INC button or touch the screen.
Next is the simple FS with LIVE SET+ assigned.
The next complex would be a programmable pedal board.
At the high end would be an external tablet or computer running software that can send the appropriate commands.

Alternate Solution
If you have an iPhone or iPad, you can run the free Soundmondo App, as a stand alone application... you can keep all of your Performance setups as icons on your iOS device. You can organize them into Set Lists. Reordering a Set is as easy as dragging and dropping the icons as you require. Recalling a Performance is as easy as touching the icon.
You need to connect your iOS device to the USB “To Host” Port.
Place your iOS device in Airplane Mode (very important, you’ll only forget once... )
You can go in any order you desire. (But you cant operate it with your feet...)

MSB 62 / LSB 0 / PC 0-15 would navigate Page 1 of the currently active Live Set.
MSB 62 / LSB 1 / PC 0-15 would navigate Page 2 of the currently active Live Set
And so on...

Thanks for that info which corrects my earlier post. I apparently missed that in my perusal of the docs.

Alternate Solution
If you have an iPhone or iPad, you can run the free Soundmondo App...(But you cant operate it with your feet...)

If he's willing to use his fingers, as you said, he can advance to the next sound just by tapping the existing screen, so my first thought was this alternate solution doesn't address his need at all... but then I thought, we don't know why he wants to use a pedal to advance. Maybe it's not because he doesn't want to have to use his hands, but rather, maybe it's because he wants to be able to advance to the next sound while keeping the MODX display on some page other than the Live Set page (i.e. the Performance page), so then this could be a way to go after all!

@Scott,
When you use the FS Assign = LIVE SET+ option, it advances through your list while you are on any screen.... you can be on the HOME screen, on the Quick Edit screen, on a Motion Sequence screen... on, literally, any screen. That’s one of the advantages of using an FC5 set to Live Set+. You only have to return to the LIVE SET grid, if you’ve forgotten what’s coming next.

The advantage of keeping the Set List in an iOS device, is the ease with which you can reorder programs.

Sorry for the delay, and thank you for all the responses. To clarify, what I'm looking to do is change performances during live performance. I will be using the MODX alongside a DSI Prophet Rev2, and I need a solution that allows me to change the presets on both, simultaneously, with a single press, and it has to be foot control. My current pedal with just the simple PC commands worked fine for that when I was using the Prophet alongside a Waldorf Blofeld, but obviously not with the MODX. I have looked into some of the larger options (like the aforementioned Yamaha MFC10), and my main issue there is the size. I play some pretty large stages where that's not an issue at all, but I also play some pretty small ones, where it can get pretty crowded up there, and that'd be difficult. I don't mind doing some programming, I can figure that out. I do need something relatively compact, though, that can handle what I need it to do. if it has an extra footswitch or two built in, that's fine (though not ideal), but a hulking behemoth on the ground isn't really an option for me. If anyone has any suggestions, that would be awesome.

The MODX has an extensive 8-Zone Master MIDI control function. I don’t know any of the requirements of the DSI Prophet but you can use the MODX to send Bank Select and Program Changes to your external synth. And the wonderful thing about the MODX is it has an A/D Input... by plugging the audio out of that synth through the MODX you can treat it not only as a MIDI slave but you can include it as one of the eight KBD CTRL Parts... you can process it with MODX Effects, EQ, you can even pre-set it’s volume so that when you recall a MODX Performance that includes the Prophet it acts like a MODX Part. You can morph to it with the Super Knob, create splits, layers that include both internal and external sounds, totally integrate it into your MODX. You can use the Prophet as an audio tempo source for the MODX Motion Control Engine, a source in the Envelope Follower, a source in the various Side Chain functions, etc., etc., etc.

Not only will you be able to advance through the Live Set with the FS, each Performance you recall can send a Bank Select and Program Change to your external devices. And by plugging the audio out to the MODX A/D In it becomes a “Part” much like an internal MODX Part!

From the MODX Zone Master FAQ...
ARE THERE ADVANTAGES IN ROUTING THE AUDIO OUTPUT OF MY MIDI 'SLAVE' HARDWARE DEVICE THROUGH THE MODX A/D INPUT?
Yes, there are several beyond just saving a couple of channels on the band's mixer:

_ The A/D signal path takes advantage of Yamaha's high definition audio path, VCM processing. It will sound great!

The MODX has an extensive 8-Zone Master MIDI control function. I don’t know any of the requirements of the DSI Prophet but you can use the MODX to send Bank Select and Program Changes to your external synth. And the wonderful thing about the MODX is it has an A/D Input... by plugging the audio out of that synth through the MODX you can treat it not only as a MIDI slave but you can include it as one of the eight KBD CTRL Parts... you can process it with MODX Effects, EQ, you can even pre-set it’s volume so that when you recall a MODX Performance that includes the Prophet it acts like a MODX Part. You can morph to it with the Super Knob, create splits, layers that include both internal and external sounds, totally integrate it into your MODX. You can use the Prophet as an audio tempo source for the MODX Motion Control Engine, a source in the Envelope Follower, a source in the various Side Chain functions, etc., etc., etc.

Not only will you be able to advance through the Live Set with the FS, each Performance you recall can send a Bank Select and Program Change to your external devices. And by plugging the audio out to the MODX A/D In it becomes a “Part” much like an internal MODX Part!

From the MODX Zone Master FAQ...
ARE THERE ADVANTAGES IN ROUTING THE AUDIO OUTPUT OF MY MIDI 'SLAVE' HARDWARE DEVICE THROUGH THE MODX A/D INPUT?
Yes, there are several beyond just saving a couple of channels on the band's mixer:

_ You have an [A/D Input On/Off] switch available on the front panel. If ever you need to cut audio for the external device you can at the touch of a button. Great for those "on-the-fly" type users.

_The A/D Input "Volume" can be pre-set and controlled on a per Performance basis. Balancing volumes of internal and external slots for complex layers and splits, can be stored and accurately recalled; Realtime control over A/D volume can be assigned on the Common/Audio level of editing in MODX and varied via the AssignKnob/Super Knob system... meaning you can morph and crossfade between internal and external sounds same as you do with the internal MODX sounds.

_ The A/D Input can be assigned it's own dual Insertion Effects per each different Performance. It's signal can be merged with the MODX to the Main L&R Outputs. Parameters of the Insertion Effects dedicated to A/D Input can be assigned to realtime Control same as any internal synth Part.

_The A/D Input can be used as a modifier (modulation source) within the Motion Control Synthesis Engine. The A/D Input can be routed via the MODX Side Chain Modulation feature to the Compressors, Dynamic Effects, Vocoder etc. adding a new dimension to your musical performance.

_ The A/D Input can be used as a tempo source for all clockable functions within MODX. Great if your external device has any kind of automated rhythmic functions. By setting MIDI SYNC = "A/D IN" MODX will sync all clockable functions to tempo it derives from the audio source connected to the analog inputs.

_ The A/D signal path takes advantage of Yamaha's high definition audio path, VCM processing. It will sound great!

This is very cool, and I was not aware of some these options. Unfortunately, that still leaves me unable to go both backward and forward with a footswitch.

MODX doesn't have a backwards/forward (both) option directly. You'll have to solve this with external gear. External gear is a big pool of possibilities. MODX does support the means to enable external gear to realize both up and down with a footswitch connected (wirelessly or wired) to this external gear. Not sure if all of the pieces are there in a "here's your solution" form yet.

The easiest/cheapest way I could my own "here's my solution" to satisfy this would be to use a PC - because it's easiest for me to churn out quick "programs" - and use a wireless keyboard to serve as my buttons. I could solder up some momentary switches (rugged) in their own rugged case that were wired to the keyboard so I could stomp on something solid and the keyboard would just be used for the RF transmitter and scancode encoder. MIDI could be transmitted to MODX using ctrlr as the MIDI interface and development environment. Keyboard input would control to signal to go to the next or previous setlist and the PC would keep track internally of which setlist entry it "thinks" it's on.

The wireless keyboard part could be miniaturized by using one of those small pocket keyboards. The footswitch solution would be no larger than existing commercially available ones.

There are probably "set list" apps out there that support commercially available page turner foot switches with up/down that let you send MSB/LSB/PC combinations. Probably an existing solution floating out there somewhere on an iOS, android, or PC/Mac platform. Something like iSongBook with Airturn can probably handle this task. There are lots of similar options out there. iSongbook allows for sending MSB/LSB/PC and even system exclusive or other MIDI message types.

Page turn interface (footpedal) support is probably something worthwhile for the iOS Camelot to think about adding in the future.