I was studying to be a gunsmith at one point, and it was my understanding that ATF took a hard line against unlicensed 'smiths. You could be correct, though.
I think if I were the dealer receiving the gun, and I knew about this up front, I probably wouldn't want to be involved. JMHO though.
That said, if this were, say, a gunstock that were getting, say, a new recoil pad, I'm not sure that it would matter, if just the stock were shipped. Maybe it does, but I don't see how you'd log it.
At one point, ATF was considering the possibility of creating a license specifically for 'smiths, which would be a good thing for this individual; however, I don't think it went far. It's too bad, really, that there isn't such a thing; it would help to open the market to some good work.