I posted this in the wiki but I guess it's not technically an exploit. Anyways if you are like me you hate cass's cowboy hat and veronica's hood, so here's a way that i figured out that removes them.
Open the inventory for either follower. Place the items "Ballcap with Glasses" and "Recruit Helmet" in their inventory, then back out so they equip them. Open their inventory again and place sunglasses in their inventory and remove the Recruit Helmet. When you back out they will equip the sunglasses but not have any headwear on. If you remove the sunglasses or the ballcap with glasses from their inventory, they will re-equip their default headwear. It will revert to normal when you load a saved game, so you will have to do it each time you start playing.
hope this helps out some people that hate their hats as much as me.