Actually, all I did was hexedit the original files and change the internal referenced names so the game thinks set 0 (underwear) is 00 (starter set) and vice versa.
I'm assuming you mean skin as when you aren't wearing anything. I don't know of a way to swap those yet, since they reside in different files. I haven't tried yet either, but their structure seems different from the main armor files (with 0-18).
@max54
As far as I know, the underwear was never used as a part of the game (in any version). I figure if it was, there would be more screenshots of people in their undies, whereas all I'd seen was renders from outside the game.
Also, it's worth noting that many NPCs wear armor from the PC armor file.
View attachment 475
no mean as skin on the armor im wearing. so that i see the curtian look but still wear a armor