Sam, the Chachamim prohibited blowing the Shofar on Shabbos (for example). That is because of a Chashash. Don’t compare that to targeting the Mitzva directly. Besides, this is a Momonus directive. You would need a Hefker Beis Din to undo it.
The problem is that even a will can’t really do away with the Bechor part. That is a Lav of Lo Suchal Levaker. It would help to give to his daughters.