Yes, I also shimmed the frog flangeways, and as others said, using the NMRA gauge is critical. Flange depth doesn't matter, we could run our trains on G scale rail and they'd work fine, as long as the gauge and flangeway widths were correct.
The outside (stock rail) guardrails prevent picking the frog. If all you want is to keep the trains from derailing, that should do the trick. If you still have some pizza cutter flanges, it certainly should work.
Shimming the frog (wing rail) flangeways won't prevent derailments, but it will narrow the gap between the end of the closure rail (from the points) and the frog. That will minimize wheel drop, even with small flanges. BUT, and this is critical, all of the wheels must be in gauge, and the flanges can't be too thick to fit through the flangeway. Depth doesn't matter.
Most wheels made for the North American market will work, although I'm not sure about Bachmann, since I don't own any of theirs. Kato and MT pizza cutters go through my modified turnouts with no problems, although some of the Kato wheels needed regauging.
