Cold set and forget it. It's totally reversible, in fact, you don't need to reverse the mod to put a 126mm wheel in. Just do it.

I was somewhat reluctant to cold set my frame, even though it's so beat up many people would probably refuse to ride it. And furthermore, I've probably cold set frames more than that when they were new. Anyway, it's 2mm per side, which is nothing. As someone said above, on my frame, I could easily have left it the way it was and just pulled the dropouts apart when I put the wheel in. My commuter bike needs more work than that to get the wheel in.