That's a question for your tuner. If they put you on the bleeding edge of the target fuel grade you're going to have problems when you step down. If you were more conservative then you probably have no worries. You could ask the same question of 93 vs 92.
There are folks that do both: one tune that works reasonable across the spectrum or two (or 3) tunes that are preset for each change. I believe E85 goes through 3 steps in grade between summer and winter to retain starting and driveability. There are tuners who have played with E85 and people who have driven on the stuff year round, so it's perfectly doable if you want. I think you may prefer more than one map that you can switch between as needed, but I know some drive on catch-all tunes that work year round, likely with side-effects to some degree.
