Anneal, recut,,recase harden. Trying to do much more than cut a couple of touchup lines in the work w/o annealing will only lead to a sloppy looking job or matchup (unless the piece is one of the 'colored, but not hardened' variety). Yes carbide gravers will cut through the case but as said the cuts will not look as smooth as the original. Any after polishing, burnishing to smooth out the new work in an attempt to match in with the old will destroy the colors your trying to protect anyway. Very fine cuts that don't pierce the case will be nothing more than misguided scratches in the surface as the tool skates over the casehardening. Tool breakage cutting thru C/H can be frustrating to say the least even with carbide. Being a professional tool sharpener is not the new job status a firearms engraver seeks.
Then there's the after effect of all those bright new cuts that must be colored somehow to match the existing old, aged cuts. Cold blue coated with some gummy shellac anyone??
