There are still things in this game that NPCs have that we dont, so I would say no, you wont be able to do that. That is just an educated guess from what I have seen in this game over the years.
Many signature characters have custom designed costume pieces. They were not made to scale with the costume generator size sliders, so they can't be used by players.
I just received a twitter from the Comic Con showing Desdemona. It made me notice something. She has one arm bare and the other gloved.
Does this mean we may be given the costume choice to mix/match gloves? I like the look and have an alt I wanted to do that with but did not see that as an option.
Hopefully, Going Rogue or Power Spectrum is adding some costume options we did not have previously.