I can grind it out pretty easily with a dremel I think. I just didn't want to do it without finding out why the tabs are there. I have never seen a box with tabs in those positions in addition to the corner tabs.
I'd apply some Dumore or other hand grinder to it. I can't say I've ever seen anything like that so perhaps someone got a little too creative. Replacing it will be advised if you can't grind the obstructions away and still have a safe switch box.
That looks like a flat mud ring on a 4" box.