A swap from a 332/3 to a 75/76 isn't possible. They wouldn't have a crew in MAD to work/fly the aircraft back to PHL. When they downgrade an aircraft in the schedule it takes two extra days to position a crew to work the return aircraft (unless they schedule the aircraft to overnight with the crew).

It is possible that they downgrade you from a 333 to a 332 but that is also unlikely. The aircraft are spread pretty thin with 3 or 4 330s out for new paint.