Try this: Right click on the Track and from the drop down menu select -- Track Actions\Set Track to default settings
Hmm, curious ... that works on the lower number tracks, but didn't on the soloists track ... I think that's probably because the soloists track has players set vis F5, where the others don't. I can test that ... OK, if I set a RealTrack via F5, the earlier track also will not clear it with set to defaults. Removing the F5 RealTrack settings does then allow set to defaults to work. The mixer description only changes after a regenerate, which explains some of my earlier confusion.
I rather expected the Mixer's display of soloist details to follow the soloist playing, but it seems just to stay permanently at the first soloist. No issue, but a shame.
At the moment, when I do things with it, BIAB now mostly does what I expect, though I'm still a little uncertain about which "this" overrides which "that" under which circumstances. Sticking with the F5 method alone seems pretty consistent and robust. I'm sure I'll trip over more things in the future ... MIDI supertracks are probably waiting in ambush :-D
It probably time now for me to save this track away and begin another to help me properly lock the process into my head and make sure I really do understand how to do these things.
Thanks everyone for your guidance. It's been really helpful.