Just bought MODX6 and can't get my Roland A-50 controller to change saved performances in the live set.

Not sure what this means - if you are talking about the MODX's LIVE SET feature, you do not need to do anything with the Roland A-50 to save MODX Performances to a Live Set.
Call up the MODX Performance you would like to place in a User Live Set
Hold [SHIFT] + [LIVE SET]
This will "register" the Performance in the first available USER Live Set slot... a white highlight appears. Touch the box you would like to place this Performance.

Once you have registered a Performance in a Live Set, the Live Set slot you place it in determines the MSB/LSB and PC for that Performance. This allows you to replace a slot with a different Performance without having to edit your controller. You want to recall the MODX Performance using the MSB/LSB and PC for the LIVE SET Slot that you have placed the Performance in... You can have 256 Live Set Slots per USER Bank.

It changes in performance mode but iI need to use my save performances in the user banks.

The MODX is always in Performance Mode. If you have placed a MODX Performance in a USER Live Set slot, and you activate that USER LIVE SET Bank, then the very first Performance in USER Bank 1, PAGE 1, Live Set Slot 1 will be recalled by MSB = 62, LSB = 0, PC 0 (or 1 depending on what convention your Roland A-50 uses 0-127 or 1-128). The second Performance, the one in USER Bank 1, PAGE 1, Live Set Slot 2 will be recalled by MSB 62, LSB = 0, PC 1 (or 2 depending on what convention your Roland A-50 uses 0-127 or 1-128).

There are 16 Slots per Page.
There are 16 Pages per each USER Bank.
There are 8 USER Banks.

Is there a way for the preset performance be switched to user like most other keyboards?

Again, not quite sure what you are trying to ask here. But like most other keyboards when you press [STORE] you get to store the current Preset into the User Bank. Is that what you mean... or do you do it differently on 'most other keyboards'? This is not really necessary with LIVE SET... by listing your PERFORMANCE in a LIVE SET - it has a different Bank Select and Program Change especially for its Live Set location.

There are some unclear pronoun references which makes the post a little difficult to decode. Let me reflect what I think you said then go from there if you let me know somethings off.

You're using a Roland A-50 (a keyboard which happens to have polyphonic aftertouch) to MIDI control your MODX. You want to use the A-50 as a master to send MSB/LSB/PC messages to MODX so that MODX responds by changing Performances which are part of your Live Set.

That's about as far as I can (first sentence) before things get muddy.

t changes in performance mode but iI need to use my save performances in the user banks.

Assuming that "it" is MODX (not sure) - I have to say that MODX only has one mode - "Performance mode". Maybe if I twist around this to make something that makes sense to me - I would translate this to: "I can recall factory preset performances, but I need to recall my custom user performances."

To recall user performances (through MIDI), there are two ways. You can either recall them directly with MSB/LSB/PC combinations (sent from the A-50 - if you can) to MODX. If you cannot send all three (MSB and LSB and PC) - then you will only send a partial combination which will use the current MSB/LSB/PC to start with and only change what you can send. If you currently have a factory preset loaded and only send a PC - you will not be able to recall a user Performance. User Performances must be addressed by sending an MSB of 64, an LSB of 32-36, and the PC 0-127.

The other way to address User Performances is indirectly by recalling Live Set slots. These you address using an MSB of 62, and LSB of 0-15 and a PC of 0-15.

It should be possible to access a maximum of 16 different user programs if all you could do is send PC. You would modify your MODX settings to default to Live Set. This should assume an MSB and LSB pair of 62 and 0. Then you could send PC 0-15 to select among any of the first 16 slots in Live Set. Unfortunately, the organization of Live Set to MIDI mapping doesn't help you much in the case where a controller can only send PC. If MODX allowed for PC 0-127 instead of the current organization of 0-15 - then you would be able to address 128 total user slots.

I believe the A-50 can only send a Program Change and not MSB/LSB. This limits the A-50's ability to only address 128 different external "programs" where modern equipment offers many more than 128 total programs (user and preset content). In order to facilitate this expansion in content, MODX uses MSB and LSB pairs.

If it is true that your Controller does not send Bank Select MSB/LSB, it will not be a sufficient controller to work your MODX, remotely. It must come from an era where all sounds of the synth were in one Bank (128 Programs). There are literally thousands of programs in the MODX... the max a Bank can hold is still 128, so you can imagine the MODX has lots of Banks! You’ll be better off operating sound selection on the MODX... Use the A50, principally, as just a set of keys.