Just open up their inventory, take all the stuff you don't want them to wear/use, give them the stuff you do want them to wear/use. I have to do this to Boone all the time, he always loots such garbage from our kills.
But I want them to wear stuff with no DT sometimes so that their appearance fits the role I want to play.
And with Veronica for example it isn't possible as her default clothing has a certain DT and she won't change into something with lesser DT.
Sadly one can't take their default clothing out of their inventory.