In answer to the question: Do you tweak your amp knobs between songs at a gig?
My behavior has changed with my amps.
When I used channel switchers, everything got set up during rehearsals and the only thing that changed during a performance was the master volume - and that usually only during sound check.
Now I use a single-channel non-MV amp, and I'm likely to turn around and tweak whenever I think I need to. With four knobs, there's not much that can go wrong.