You should be fine with 91 octane. You definitely do not want to re-flash that tune. If it was done in Florida at a group day, the owner dropped in the neighborhood of a grand for the custom tune with dyno time and everything. If I remember correctly, that car has a NW CAI and a 178 pulley (or was it Code 3?). Either way, with that tune, the car should run like a raped ape. Try to remember to do a TB reset before you take off on the trip back, and just try to wipe the grin off your face.