The original serial number is not on the heel. Trust me, I won't be devaluing anything.
My question is mainly about technical feasibility, not legality. M1 receivers are generally made with pretty hard steel, so I wasn't sure if that would give CA's laser engraver problems.
It's technically possible, but no engraving serial numbers unless you have permission from the ATF to do so. It could cut the receiver in half if we cranked it up and told it to do so... steel is no problem at all.