Thanks to everyone for ALL the great help! I hadn't discovered the function to enable/disable style, so that explains a lot. Someone asked me to give step-by-step details of what I did. That would probably be "the blind leading the blind". So instead I'll try to summarize what I SHOULD have done.

For a little background, the song I'm working on is Beatles' "Yesterday". I had created a pretty accurate version of the string part, using the Finale program, and printed out music for me to play live with our classic rock band. Then I wanted to create a BIAB version for my solo guitar/vocal performance, using that string part. I went back to Finale, transposed it to my vocal key (had a tenor singing it with the band), and created a midi file. Then here is what I think I SHOULD have done:

Find or create the basic BIAB file, which would have bass, drums, melody, chords. Then use the "Import to Soloist from Midi" function to get my string part into Soloist.

Instead, I started out with "Open Midi", which put the midi part into the Melody, apparently with some random style, with style disabled. Then I had to move the string part from Melody to Soloist, and stumbled across the feature to enable style.

The only lingering problem I have is that the volume control for Melody doesn't seem to function for the song now. Just always max volume. I noticed this with the midi part when I imported to Melody; so now seems to be a holdover from that which has the volume control for Melody disabled. Any ideas about that??

Thanks again, everyone!