how does one regenerate a single track, better yet just a section of said track

If you are happy with all the other tracks, freeze them. Then regenerating the song will do only the one track you want.

BIAB cannot regenerate part of a track. Yes, it has been requested. But, RealBand can! In BIAB, your only choice is to continue to regenerate until you get what you want, and then freeze that track too.

Cool, thanks. The problem I'm having with realband is that it doesn't seem to recognize the shots and holds

Are you using RealBand or Band-In-A-Box?
Changing a chord, e.g. adding Shots or Holds, will not work on already frozen tracks.

The BIAB tracks weren't frozen when I opened song in RealBand, it seems to work fine in reaper

Frozen only stays Frozen while in BIAB. When you transfer (in any manner) to your DAW or to the BIAB-VST or to RealBand, the tracks will be "audio or midi" and will not regenerate. Does that make sense? Or have we drifted off topic? The question seemed to be "no shots or holds" when BIAB is opened in Realband? For that question I don't have an immediate answer.

What version of Band-in-a-Box are you using and what build number? Had you tested with other song project files?

we had just did a quick test in Band-in-a-Box 2021 (833) by using a Style with a combination of RealTracks and MIDI tracks. There was a different type of shot and hold every other bar, then we saved the song and re-opened in RealBand64. The shots and holds do appear to be there in RealBand64 this test.

You could also freeze your tracks and send us a copy of your song for testing to support@pgmusic.com.