Firing pins are pretty easy to swap out, though. Easy enough that this could be used to tamper with evidence or even frame someone. It doesn't really seem like a great idea.
Micro stamping is currently not enforced strictly but if it would it would be no more legal to swap the firing pin as it would be to put in a full auto fire control mechanism on a federa level, or on a state level flash hider or a normal capacity magazine in states that forbid them.