One of the bummer about converting round to square is that you loose a good portion of your cutter if you lessen the top plate angle, which I do because it holds up better in hardwoods and for work chains.So finesse and no fatigue is key when using a file? I like it! I've never converted round to square myself. Though I've often thought it wood be easy to do with a grinder, and like you said. A little at a time. Makes sense to me!
The way Mike is describing is the best way to not waste the cutter and thus get the most usage out of your chains, and to get a fast efficient & very smooth cutting chain.
I have a few more square chains to grind, if I remember I'll grab a round chain and take some pictures converting a cutter over to what I like for a work grind. I'd much rather grind them with the price they are getting for files right now, it's ridiculous how much they've gone up, sure hope it's transitory .