Following the advice I've received here, I'm doing all my new-work wiring in deep, 4" square, metal boxes, and I'll be placing single- or double-gang mud rings on them for mounting devices.
I would presume that I should install the mud-rings before installing the drywall, then cut out the drywall to the appropriate exposed gang size.
However, I got to thinking (as I sometimes do) that this means that the screws that hold the mud ring in place are semi-permanently buried beneath drywall and, if I should ever need to go from a single- to double-gang at this location I'd be doing drywall repair work. To avoid this issue, I could install the drywall then cut it around the 4" box, but that would probably leave me with a hole in the drywall larger than even a jumbo size wall plate would cover, especially if it's a single-gang.
Am I correct in my presumption that I am to install the mud-rings and bury their mounting screws under the drywall?