The time we need to change my ds when he was 1. The SW flight attendent brought us to the back of the plane and we put the changing pad on the floor in their kitchen area.
Funny thing happened after we rushed to change his diaper. Well I didn't get it right & the diaper leaked all over me on the magical express. My wife found it extremely funny.
Yep I've changed diapers here to. Or some planes have a large area at the back outside the lavs with a seat for the FA.
Leaving the door open does help
I've never had a FA object in fact many have suggested it.
If it is a dirty diaper it is best to double bag it so it doesn't smell up the plane.
The worst is if it happens and it is a flight with a lot of turbulence and you can't get up.