It will just substitute with what chords you do have.
If you use the Pop template and add more chords and keys that you would use as they just have Keys A C E G.
If you play 1 bar phrases on the lest common chords maybe so there's no held notes into another chord ?
The common progression you can play over and link them in the usertrack bar settings.
Or how I suggested in keys (with Drum in the filename) then if the Bar to Bar regen and change UserTrack F5 are added you can put it together how you like.
This was a Flute in a RealDrum but you can do the same with a UserTrack
https://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=521931

Biab Track Injector for Reaper
Free Biab Chord Picker Tool