I would just shoot them an email to ask them if they would be cool with whatever wardrobe options you had in mind. I have bought wardrobe for past customs, but that was with Sleeperkid and FemWrestlingRooms. I don't know how places like NEFW and Slamminladies would be with that. Though I would say that NEFW seems like they would be open to it.
Obviously, I can't speak for everyone, but I would probably assume that most of the wrestlers themselves would probably be ok with custom wardrobe as long as it isn't anything ridiculous. But like I said, most of these sites are pretty good at responding to emails, so I would just try contacting them if you are seriously thinking about a custom.