There is a slightly alternate form to do this, though it's not often used. It's not used because the normal method is exactly as Darth Parametric described. In addition, it relies on knowing the tag of the footlocker in question (which in this case is "end_locker01") and knowing the order of the spawned objects (if there's more than one object with that tag).
In this case though, that is literally the only time that tag is used. So we can do this: remove the basic clothing item from the footlocker and then add whatever we want to it. I'll re-use the sub4 I posted above, but modify it like so: