Chicago...
This is available.... If you have current version.

Press ALT+F8 select a bar, select a track that you want to regenerate and you will just regenerate content of that particular bar, leaving all others intact. And you can try out a few different regenerations, see what works best. You can even, in most cases regenerate a segment of a single bar.

P.S. This is probably among top 10 features BIAB introduced in 5 years I was here. I use it on almost all of my tunes.