As a previous Orbit owner, this isn't that big a deal. Just give the belt about 30 seconds to "shrink" again and your off and running. Honestly, when switching back to 33 after 45's, by the time I got my next 33 picked out and plated the belt was perfectly fine.
I've managed to get the "flick" from 45 to 33 a few times while everything's spinning. Most of the time, though, I just slowly pinch the belt and let it relax back onto the 33 groove of the motor.