I swap inserts willy nilly on my gen and reps alike. I can't get the caseback off my gen, even with a high quality hand tool with Rolex sockets. It needs a pro bench tool. Last time it was serviced it was put on mega tight. Probably a good thing, as I really have no business poking around in there anyway. I swap dials, bezels. movements, hands, crystals on reps to suit my current fancy. I just ordered about 8 inserts over the weekend for some upcoming mods, haha.
A gen dial can fit in a rep if the rehaut aperture is not too large. Gen dials (GMT, Sub, YM) are usually ~27.3mm. Rep dials are often larger so the rehaut has a larger diameter, sometimes too large to accommodate a gen dial. If the rep has an ETA movement, the gen dial feet need to be clipped and new feet glued or soldered on. This devalues the gen dial, even if the process is reversed. For that reason ppl choose reps with clone 3135 movements for Frankens.