BATF(E) ruled long ago that if you were performing any operation that might result in the elimination or alteration of the serial number, that a paper record of the number and the availability of stamps to restore it (perhaps elsewhere on the weapon, for example if round butting a S&W revolver) was sufficient to avoid prosecution.
If you can recover the original number, I expect that making it more legible really isn't an issue.
I'd like to see that ruling,,sure would make things easier.
On compliance checks, the Agents always pound the point home about not haveing a gun with ser# problems and never altering/removing/etc the ser# on any firearm.
What I and other gunsmiths/engravers have run into is that if you want to move the serial number to another location on the gun(frame), or if any operation you're doing will remove any part of the ser# so that it will require remarking,,prior BATF approval is required before the operation is done.
They just do not want you to touch that mfg'r applied ser#.
Bowen used to put lanyard swivels into the butt of S&W revolvers and move the serial # to the side as the factory did. He went through the proper steps to get approval, etc.
More recently that approval has been denied and he no longer does that mod.
Another is the lightweight SAA he builds with weight reducing cuts to the forward sides of the frame. No problem on a Colt,,but on a Ruger, the ser# is stamped on the right hand side.
He won't do those cuts to the Rugers because of the problem getting approval to move the ser# to another location on the frame.
I applied for permission to move a # on a commercial P38 being engraved. Denied.
It was even put in doubt wether I could gold inlay an existing ser# on a gun. That was during a compliance check many years ago. I had to wait for permission to procede or have the shotgun confiscated!
You never know how an Agent will react to what they see in front of them.
I've seen plenty of guns where a 'smith simply restamped the old # in a new location and all seems to be well with the world.
We see it all the time.
But there has been a procedure in place to do it properly and legally. The problem was/is the cumbersome procedure and no guarentee that your request will be granted.
If there is a ruling more recent makeing the procedure easier and with no paperwork, permission request, ect., I'm all for it.