What do u mean raised boss?
Look at the backside of, say, a Leviton duplex receptacle cover, where the screw goes thru the middle. You will see a little 'donut' (or raised boss) of plastic there. If you
carefully trim that away with a razor knife, the entire backside of the cover will all be at the same level/height. The receptacle will stick out the the cover a bit, but the cover might wind up flush to the wall, w/o tearing out sheetrock. You can do the same with switchplates, you'll just have 2 pieces of plastic to trim per gang. Unbreakable covers have to be used ofc, but imho they should be used anyway.
If that doesnt take up the slack caused by the mudring sticking out, you are pretty much gonna have to tear out the sheetrock to fix it.