An alternative could be to create individual files for each part of your song like suggested below:
4/4 part 1 as songx4by4part1.sgu
3/4 part 1 as songx3by4part1.sgu
4/4 part 2 as songx4by4part2.sgu
.
.
.
ect
Finally take all you parts and export them into a DAW Pro Tools or Logic ProX or similar and then stick it all together in your DAW.

It's a slow process, but for me it provides me full control of each part of the song, and if I'm not satisfied with the rendering and creation from the Real Track algorithm, it takes less time to re-render each part/section of the song.

I used this method, when BIAB2016 was very little cooperative mixing Real Tracks and Midi in the same file, and actually have adopted that method permanently.

(If PG Music staff is now banging their head against the wall in frustration I fully understand it - customers are not following the most elementary logic) :-)

MacMini M1 - BIAB2021 - Logic Pro X - iZotope Music Production Suite - Scaler 2 - far too many Waves plugins and Line 6 Guitars and boards + a fantastic Yamaha THR10ll mini Amp - Avid MBOX Studio

Peters' Garage is available on all major streaming services