Well, in the manga we've already seen Chrona in more out of uniform clothing, i.e: The White Suit at that party thing before the archane arc.
But we could argue about Chrona's gender all day and there really is no point. Let's just say Chrona's gender is up to the individual until it is actually announced if ever. I personally like Chrona male/trap, but it's really up to you.
Anyway, have some Soul.