Disney requests that guests over fourteen not wear costumes at all, but costumes that resemble any Star Wars character are especially warned against at the new Star Wars Galaxy’s Edge attraction. You can’t even wear the Star Wars costumes you buy from the park itself. This is pretty unfortunate for guests that wanted to dress as the galaxy’s best bounty hunter or a robed Jedi, because that’s a big part of the fun. But even though its disappointing, there is a fairly good reason for it.
Imagine this scenario; you see Darth Vader wandering about, and ask him directions to one of the attractions. He offers to lead you there, and you accept because he’s obviously a park employee. But then he leads you somewhere secluded and robs you, because he was never a park employee, just some stranger in a good costume.
This example is quite extreme of course, but the overall point still stands. It’s really hard to tell who is a guest and who is a park employee when everyone is dressed in a similar fashion: as if everyone in Best Buy was wearing blue shirts and khakis. It’s unlikely that you’ll get robbed in Disneyland (at least in the criminal sense), but confusing a stranger for a park employee thanks to his excellent Star Wars costume is still a concern. They could give you bad directions, vulgarly photobomb your pictures, or just generally be a nuisance.
Of course, maybe Disney just doesn’t want people giving Star Wars and its characters a bad rep now that they own the franchise. Regardless, ‘Disneybounding’ is still permitted. Disney itself outright says so:
“The current Disneyland Resort costume policy will be in effect in Star Wars: Galaxy’s Edge. Costumes may not be worn by guests 14 years of age or older. Appropriate Disney bounding — dressing in outfits inspired by favorite characters — is permitted.”
Disneybounding is unfortunately a poor substitute: the idea is that you build an outfit of everyday apparel that makes use of the overall color scheme of a character, rather than outright dressing as that character. That’s certainly not as fun as a full on Darth Maul getup, but at least it’s something. Then again, there would be some serious questions to ask if Disney could go so far as to tell guests how to dress in ordinary clothing.
Either way, while this rule is unfortunate, it’s also quite understandable, and we can’t really blame Disney for having it in place. Though it does seem a little rude and pretentious to sell outfits that the guests can’t even wear within the park; unless you’re under fourteen, of course.