Didn't the Great Movie Ride have a couple different costumes depending on where the CM was working? (Obviously ignoring the hijackers) The tour guides had one costume, the load platform had another, and didn't the CM's working in the courtyard have a third? Does anyone know how cast rotations were handled there?
As for RotR, it may be reading into it a little too much, but there was that pic of Iger and other top brass and WDI folks posing in the hangar bay with RotR CM's in costume. Since this was a couple months ago, presumably those were the trainer CM's. And if they were hosting the top brass, they may have been running the attraction with the full staff needed to at least operate the attraction.
[Minor spoilers for anyone who doesn't want to know a single thing about RotR]
In that photo I count 5 First Order CM's in black and 7 Resistance CM's in brown. This ratio fits, since it seems the FO CM's ("FOers"?) are only there to shepherd the guests from the shuttle through the shuttle bay to the holding cells. Everyone else in preshows, loading into the shuttle, getting you into the ride vehicles, unloading you at the end, etc are all Resistance personnel, so there would obviously need to be more people in those costumes.
One of the Resistance CM's is wearing a different coat than the others. He's also wearing a cap with goggles on top. Perhaps this is a specialized CM position in the story? Perhaps a flight crew type person who loads guests into the shuttle? (There's a second Resistance CM with the same cap and goggles, but in the same vest as everyone else, so not sure what to make of that) Is there a CM in the shuttle with guests? Or will it be entirely the show and AA's? Perhaps it'll start with a CM in there and eventually it'll become the "Chris" of the attraction...
One thing I will say, there does not appear to be any crossover of costume pieces between Resistance and FO. Even the shoes are a different color. So I would hope/assume that every CM is issued both versions of the costume and locker rooms are available in the cast areas in case they need to change rotations midway through the day.
-Rob