I always used ARP SELECT 1-8 to switch between them. Since you can assign arp transition to the measure, this gives you some slack in when you have to press the ARP 1-8 button before you would miss the natural transition point.

I do hear you about the desire for automation - I'm sure there's something. A little pressed for time to look it up at the moment.

Reviewing old questions and found this... we get many requests that want to make the MONTAGE Arpeggiators act more like the Style Engine in an Arranger. For those that are not aware, Arrangers make easy what is described here in the original post. Because the instruction to play the Fill-in will also include the information to transition back to a Main Section. Thus eliminating the button dance.

The MONTAGE Arpeggiators do not have that same type of automated movement, so a press, before and a quick press during, the Fill-in becomes necessary, if attempting to do the same thing. Because the focus of Arpeggiators is toward *recording* their Output to a plackback device, the automated section movement is not implemented to the phrases or buttons themselves. Once selected an Arp continues to cycle, until it gets another command.

While the fact that a FILL-IN automatically returns to a main section, or automatically advances to more complex/less complex section is perfect for the “Live” performer, it is not ideal when the focus is creating/assembling your own. Here’s what I mean, in a situation where you have a 32-bar structure, AABA... you might create 2 eight Measure Sections and 2 one measure Fill-ins to make the transitions A-to-B, and the fill-in to return to A.

Play 7 measures of A, trigger Fill-in ‘return to A’
Play 7 measures of A, trigger Fill-in ‘A-to-B’
Play 7 measures of B, trigger Fill-in ‘return to A’
Play 8 measures of A

In the Style engine a Fill-in has a built in destination so once it is requested (by pressing the Fill-in button) the transition to the next main section is guaranteed. Nothing to do *during* the fill-in Measure... with the Arp engine you must navigate the “button dance” which is often untenable if you must also perform.

When recording the data to the Recorder or a DAW, there is no pressure to have to perform simultaneously... you are typically laying down your backing tracks ahead of performing. This is the way Arps are traditionally used... Record them, then you can manipulate them in any number of ways.

What you can do...
When attempting to use the Arpeggio engine ‘like an arranger’ try to include the fill-in in your section. This way you are not going to have to do anything in that “one measure window” of time. Instead of triggering a fill at Measure 7 so it occurs in measure 8 and then again during the fill trigger the next main section... create 8 Measure sections that include the fill-in as Measure 8. Or begin to rethink what type of real-time re-arrangement you actually need.

This may require re-recording Drum Arpeggio and creating a custom User Drum Arp to fit what you need.
That is a possibility. We may visit this topic, in depth, as options for Drum Track Construction are always on the frequently asked question list.

I have broken complete linear compositions (songs) down into musical sections... large musical sections, this way I can reconstruct it on-the-fly. Since the intro and melody of the song go down usually in a preplanned fashion... that becomes a Section. Then I have Section that is just the Intro, repeating which I can use when I wish to extend play. Other Sections include the basic vamp over which I can Solo, I also can extend this letting it cycle as necessary... when I wish to play the melody again, I’ve got that as a Section. Another Section would be the one to end the song... and I have one that is the volume-down groove for extended ‘cool down’... just rethink how you would break the composition down... the goal is still FREEDOM of real-time rearranging... but by using larger musical chunks as your Sections, you will not have to “work so hard” manually pressing Fill-in buttons. Work those into the larger sections so that occur where needed. Once you do you stop worrying about them so much.

Just a thought.

Also when thinking about automating the changes of Arp Selection... Arp Select can be included in a Scene. Scene recall commands can be documented Out via MIDI as either System Exclusive messages or as CC messages on MIDI Ch1. You could record yourself pressing the Scene buttons — this can then be played back to the MONTAGE.
To link an Arp Select to a Scene:
From the HOME screen, touch “Scene”
Turn the MEMORY switch = On for ARP in Scene 1
Along the bottom set the Arp Select 1-8 that you wish to link to this Scene.
Move to Scene 2...