Switching Challos after Lifting Them
One can explain the Magen Avraham’s position about cutting challos in such a manner, though, that it has nothing to do with the question of whether ein ma’avirin al hamitzvos requires a person to return to a skipped mitzvah before fulfilling the one presently before him. We can explain that the reason one is not violating ein ma’avirin al hamitzvos when cutting the bottom challah (if it was originally on top before the challos were picked up) is because neither challah can be considered “closer” once the challos are in someone’s hands (see Avodas Mikdash, Menachos 4b).