Change underwear?

[Lostxero]

I love the serpent sith mod, and reskined it for my char, but its underwear is the ugly bulky tan bathrobe thingy that I abhore, I was wondering if there is a way to change the underwear to the model in the gloves ( found here ) that came out for the serpent sith dude. I messed around for a bit trying to figure it out, but in the end I couldn't figure out how to change the undrwear.