Can I have chord symbols in chord symbol regions but not in every slash region? In the same part.
You could hide the chords in your slash regions, but I don’t think this can be automatic.
Adding to the reply of @Janus
Hiding can be done locally, so the chords in the part can be hidden, while they are shown in the score
I’ve worked with trebles, and I don’t think I’d want to give them that much freedom. 