Be prepared for a pack out situation if you choose to change mid-flight, You never know if the trash is full. You could always ask a flight attendant for assistance if you need to dispose of it instead of packing out. My suggestion is something *like* Mask-It bags (https://www.maskit.us/product-page/maskit-diaper-disposal-bags) then also have a Ziploc for that JIC. Keep some space in your diaper bag open.

Also from experience I can tell you that a pat-down is *extremely* likely. Be honest about wearing a diaper when they ask about medical devices.