I've flown all over North America and done many overseas trips with no issues. Day or day before flight, I put on a new appliance, because who knows, you might get stuck on a longer than expected layover, God knows where. If you're flying in coach, when they start boarding, go hit the washroom to empty. You'll be one of the last to board, which is perfect. If you're flying first class, I board first, get comfy, then hit the washroom on the plane before taxi out. During takeoff and landing is when you can't leave your seat, so you need to plan for that. Also, wherever you are going, always bring double your supplies. Can't buy our stuff at the corner store, ya know? And don't check your supplies, bring them on your carry-on... Baggage gets lost all the time. When landing, keep an eye on the air-show/time to destination. Make sure you empty once the descent starts, so you'll be okay for the landing/taxi portion when you can't get up.
If you do need to do an emergency bag change, remember it doesn't have to be perfect, wherever you are... and it's certainly not going to be if done perfectly in a confined moving space, lol. Just clean up whatever mess, slap a new one on, and do a proper change at the next opportunity like in a larger airport bathroom. Long haul flights, the bathrooms don't seem to be so small, either.
And no scissors on board! If you need to cut your flange to fit right, make sure you prep a couple flanges for your carry-on. Also, there are no restrictions on liquids/pastes for medical reasons.
As for heat, if I sweat/exercise a lot, it just brings my wear time from 4 days to 3.
Matt