If you or anyone else needs that RT 1831 as a functioning constant track pattern, now without waiting for PG to get around to it,
just enter all the one bar chords you will be using repeating them to give Biab more choice, in Biab generate up the track and regen any sections that are wrong. In Song Setting > Avoid Transpositions.
Now save it as a UsersTrack by rendering track and loading it into the Audio track, you can also make a DI version if need be.
Because you now have partial regen and can change any instrument at any bar you can also create a Holds UserTrack for it.

https://stash.reaper.fm/u/ReaTrak (Scripts for Biab Reaper)
Open SGU in Reaper Instantly