This is how I think it would work, generating in RAM:
I will use the example below using a physical wav file, you have your generated track, that is the top track in the Plugin,
the track is Frozen but you highlight the bars you want re-generated,
that section is cut out of the RAM,
a new section of bars will be generated (on second track in Plugin) and merged into that section.

This played seamlessly when I tried it.
In the Plugin you can select bars and it will just generate that section up.

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Biab Track Injector for Reaper
Free Biab Chord Picker Tool