So here's the answer from Roland Product Support:
Roland Product Support (Roland Corporation)

Nov 3, 2023, 3:41 PM PDT

Hello,

The Prelude and GW-8 do have "Performances" which save the Upper and Lower tone information and rhythm data to be recalled later, but there is not an option to select these via MIDI. You can select the Upper and Lower tones using bank select and program change messages, but there is not an option to select Performances this way on these models.

There is also not a MIDI message that can advance up or down the Performances, but you can assign a footswitch for this if needed.

womp, womp. I guess I'm in the market or will trade for a good used BK-5.

I played a friend’s BK-5. Felt cheap (keybed nowhere near the BK-9), sounded cheap (possibly cheaper DAC’s).

Thought you had a BK9? Why all this effort to work with an inferior keyboard?

I do have a BK9 here at home, but I want something more portable to use on vacation. I actually tried, and the BK9 is too wide to fit in the rear hatch of my car (it barely fits across the backseat!) I also think that it's too nice/valuable to risk the abuse it may encounter.

The BK7m doesn't have style editing capability, so that's out.

The E-A7 is also expensive. Although it has much advanced functionality, MIDI selection of User Programs is not expressly documented in the manuals. The E-A7 uses ten banks of ten UPGs instead of sixteen banks of eight. So even if MIDI selection of user programs is possible, the starting memory address may be different. Maybe it's worth bugging Roland Support about the E-A7 so that others will know whether it's possible to select UPGs via midi on THAT board, and how!

In the past, I've seen BK5s sell in the $3xx - $4xx range. For that price it would be a worthwhile acquisition. But I still have to sell the Prelude and some other boards that I've acquired through the years and don't play anymore.

Does the BK9 fit if not in the case? I know most 76 note cases are way oversized for the slender BK9! Only thing I found that wasn’t stupid big was a now discontinued SKB hard ABS case meant more for 73 Nord’s etc, but the BK9 JUST squeezed into. Bit too snug for flying, but fine for self handling.

I'm a home player, so all I have is a soft bag. Flying, I wouldn't even attempt to bring a keyboard. Maybe as checked baggage, but that means an expensive hard case (and a lot of weight!)

If I do a vacation car trip, there will be a lot of other stuff in the car. I would like to put the arranger in the rear hatch where it would be out of the sun, and importantly, out of sight!

I'm sure the BK5 is the best choice for this because it does everything I want and I can probably use the same UPGs on the BK9. Now I just have to trade with someone, or find one in good condition for a low price!

BK5 UPS (Performance List) data is not backwards compatible with the BK9, and vice versa. Individual styles are, but afaik, you can’t load a BK5 Performance List into a BK9, and you DEFINITELY can’t get a BK5 to read a BK9’s UPS.

There’s just too many differences between the two models.

So you definitely got some work duplicating your work. The old G70 series stored the data for each UPG (Performance) individually inside a folder of the UPS (Performance List) so you could go in and select them individually, but the BK series is just a .UPS file, not a folder.

Do you travel alone to gigs..? I used to fold forward the passenger seat in small cars and lay the keyboard front to back partly on it!