I don't know if it ever got patched, but there was an inventory glitch that allowed you to do that. I don't know if I'm allowed to detail it step by step, but I'm sure with a bit of research you could find it.
just add a hair item into a set and active it then add all the other hair items you want to add directly to set without clicking on activate, since the set is already activated the other hair items will show up in game too.
just add a hair item into a set and active it then add all the other hair items you want to add directly to set without clicking on activate, since the set is already activated the other hair items will show up in game too.