Usually 90* is the highest we recommend- a degree or 2 more may still be safe but make sure you double-check the temperatures where the snake can touch.
I hope it's just residual shed in his nostril- what humidity are you keeping him at? When the humidity is too low, that might cause this issue. Raising the humidity might help, in that case.
Keep an eye on him- and IF he does get worse (open mouth breathing- bubbling-struggling to breath- restless), get veterinary help quickly because snakes cannot really cough- they can drown (choke to death) on secretions from an RI. Hoping for the best though.