Tip from an old choral coach years ago..
keep a large cup of shaved or cracked ice flakes with a little water backstage...or for during intermissions or breaks...
Suck on the ice before performing, and if possible during quick breaks, and continue for the few hours after the performance.
He used to suggest this to soloists who would have a tickle, or sore throat or even laryngitis. I tried it a few times and it seemed to aenesthesize the throat temporarily pretty well.
Don't over do it. Too much will cover up a possible real problem.