The difficulty with being in two costumes is that it requires you to have time to change from costume A to costume B.
We can't guarantee any sort of skit order shuffling to allow multiple people to do costume changes between skits (we try to accomodate certain requests, but the tech team has difficulty with changes to the skit line up because that messes up their programs for handling sound & lighting). Also, what if you have a 'costume malfunction' while trying to get changed? You could be late for getting to your second skit.
Also, can you handle being in two skits? This means you have to memorize twice as much material, so your performance may not be a good as it could have been were you to be in only one. What happens if you get sick and can't perform? Now, TWO skits will be missing a person and may have to be cancelled
If you're going to be in a skit in costume B, but have costume A judged, the rules don't prohibit it, because the judging for costumes is separate from judging for skits. HOWEVER, we still do have the issue of you figuring out how to transform from costume A to B after you walk across stage to show off your costume entry during the walk-on time at the start of cosplay. If the costumes are designed such that you can wear costume B under costume A, then you could easily do it. Otherwise, I wouldn't recommend it.
What I'm saying is that the RULES do not prohibit you from doing it, however LOGISTICS of the event make it near impossible to manage the costume change gracefully. You'd have to get off stage, rush to the nearest rest room, strip, get dressed, fix hair, do makeup and then dash back to the green room / backstage to be ready for next time on stage.
The rule for being in two skits is that you may perform in two skits, but your name will be listed with only one group (also the second skit's group should contain different people - that is Bang Bang Neko as a group can't have two skits, but one of the actors from Bang Bang Neko could be in another skit in addition to Bang Bang Neko's skit) and you won't be eligible for prizes in that second skit.
From the rules,
"Multiple costumes made by the same person may be entered in the costume competition so long as each costume appears on a different body."
So if you get a friend to wear your second costume, then both costumes can be seen.