i believe the laws governing the stamping information required on a firearm and who has authority to change/alter/repair that stamping info is spelled out in usc 18 (available from the atf website...which is linked off the u.s. treasury website.

i was under the impression an ffl with an sot could do the job...but i may be wrong on this. some fellas on the web have stated that only the original manufacturer of the firearm can do this kind of work.

i really don't know, so you should speak with your local sot equipped ffl. perhaps asking troy sellars might get you an answer.