'I wanted to add a soloist' ..

If I open a BiaB file in RB, the first thing I do is change all BiaB tracks to regular tracks.
RB is not BiaB and I don't want it to be.

If the top 6-8 track names are blue, try the Edit-Make all BB tracks regular tracks.
Then you can act like RB is a DAW and generate what yoou want.
If you want a solo; select the bars and generate a solo using Realtracks .. or use generate Multiriff and get 8 solo tracks to pick from (or slice/dice together to make one).

I never try to make RB act like it is BiaB, too restricting for my workflow.

Make your sound your own!
.. I do not work here, but the benefits are still awesome