Is it possible to re-generate just 1 bar in BIAB? It is a real track so I cannot do an edit.
As a general rule, no. If you have the Windows version of BIAB, it includes a DAW program called RealBand. It is easy to do in RealBand. In RealBand, select the bar on the track you want to edit and Rt. Click on the bar and select multi riff. It will generate 7 regenerations of the bar for you to choose from.
Also, there are techniques in any DAW that may work if you generate several versions of the RealTrack you are working on and you are able to cut/paste a bar from another generated track of the same instrument.