Unstretching stretched metal?
Petty tough to do in the flat. Try it some time in the round.

Might want to start with a piece of copper roofing material first. Just to get a handle on stretching, shrinking, annealing, hammering, etc. Working copper is part of historic roof restoration. Steel doesn't work like copper.

I have a shotgun where the slight bulge was just filed off. Does that count as a bulge repair?

I suppose it served it's purpose. I bought the shotgun before I bought a WTG.

Out there doing it best I can.