And when it does arrive, it should open up the customisation of costumes by quite a bit. I made the same mistake when I first bought my extra slots and I really wasn't happy that they were uniform only, but I used them for uniforms anyway, and now I have about a dozen of them!
I am thinking of renaming my character to Amidala I change uniforms so often, and I'm sure I only have a Galaxy Class because the whole of the saucer section could easily be converted into a walk in wardrobe. :p
I believe with Cryptic that all sales are final. Only in extreme circumstances have I seen them give money back. Besides, they're gonna make every costume slot "universal" eventually. I say wait until then.
You can create an off-duty uniform in the new slot (or at least I could), but only if it's the first thing you do with it. Once you've used the slot for an on-duty uniform, that's all it can be used for. And once you save your off-duty uniform, you can't change it.
Their ultimate goal is to eliminate off-duty costumes as a distinct entity, and in the meantime, they're not going to fix the existing bugs with the costume slots.