When y'all are doing a job, let's say you are installing a GFCI receptacle in a bathroom where there is an existing non-GFCI duplex receptacle (by the sink), and the box is an older metallic one about 2x3 in., do you break out the old box and install a "old work" box 4x4 and use a single-gang mud ring?
Or, do you tape around the GFCI and try to cram the GFCI in the box that is barely larger than the GFCI itself?
I usually would remove the old box and replace with a new plastic old work box and use a over sized plate if needed to make up any gaps between the box and rock. As far as removel of the old box i do not make the hole any larger then it is now. i either pry the old one off with a screwdriver. or use a cordless saw. to cut it. If the old box dont fit out of the new hole i drop it down into the wall. (i try not too though). And then i just install the new item. alittle long winded but hope it helps.
I work in homes built any time during the last 100 years. I start off with discovering the box to be too small and as I figure out how to remove it, I settle on what I will replace it with. If the removal is messy, I'll move through a couple choices for the new box, and at some point settle on it and go get it from the truck. I keep a wide variety on the truck. Need I say that the truck is overloaded?
If it's NM cable you're dealing with I think replacing the existing box with a 'SmartBox' is a good solution. They have more cu in capacity than a standard PVC old work box and cost less than deep one:
The screws and supports are back further than it seems from the 1st picture. Here's another pic from a different angle. The screw block starts about 3/4" back from the front. As you can see there should be no problem getting a GFCI in there, and it's an 18.5 cu in. box.