I agree with the consensus. I change in the hotel and walk/take a shuttle to the convention center. The restrooms are filthy, so I wouldn't even change my mind in there.
If you're lucky, you MAY find an empty conference room to change in during the wee-early hours of the show, but those opportunities are few and far between... especially with "Elite" patrolling the halls. It would be nice if they turned one of the empty rooms into a cosplay locker room. I know there are a few conventions that have something similar.