The one time I did decals, I already had the rest of the game apart from necessity (boards and pf were already being reworked) so breaking down the cab the rest of the way was no big deal. And that turned out to be required: the whole time while doing the cab, being able to flip / tip / angle it - without an attached head or other hardware in the way - proved incredibly valuable. There's no way I would do another cab decal without breaking it down.
But honestly, it's not that difficult: pulling out the pf and removing the head are easy, and 90% of the requirement. The rest is basically coin door, flipper buttons, and side rails... the side rails are always the worst part. You don't need to go "all OCD in" and remove the tilt panel, transformer, and other interior bits unless you're doing a full repaint and even then, you can probably work around them if desired.
Agreed that decals will do NOTHING to hide any blemishes. The real work is in the cab prep. Stripping the parts is stupid easy, takes less than an hour (EDIT: well maybe the siderails take that much on their own, too many variables in play). Replacing said parts isn't much more difficult. But the sanding / filling / repairing / painting / touchup / cure-time waiting / etc etc etc is what consumes the time and creates the mess.