Wow! Sounds like you' having a good time. You might want to talk to Syllvia Miskoe about flying with an accordion, I know she has done that lots.
Even in a "pressurized" cabin the pressure rapidly goes down from sea level to 8000' level pretty quickly, and then up again when you land. I would be concerned whether this would hurt the bellows, unless there is some saftey valve you can open.
I personally would not fly on any airplane where there was known to be any accordion present, it would surely attract terrorists--
MD