That's certifiably not fun :(

Not that one ever should have to do such for medical equipment, but wonder if someone could grind down the firmer stuff on the first new mold, assuming it was kept...

(Not really useful anecdote:) I remember circa 25 years ago, my audiologist had a benchtop grinding/buffing wheel that she'd take the earmolds to a few times when modifications were needed. Even at that young age, it was clear that grinding soft materials didn't work very well.