So if you are a regular kilt wearer (and particularly if you see it as part of your identity) why would you wear one on Halloween as a costume?
To start with, I can't see using what I wear as a part of my identity. That just seems a bit shallow to me. In any case, If I were to wear the kilt every day, then wearing it exactly the same way I did every day would not, likely, be seen as a costume. On the other hand, I very rarely wear a kilt, Jacobite shirt, eye patch and cutlass, so that would be seen as a costume.