Same thing happens when trying to modify pawns. It’s an incredibly glitchy system. The issue there stems from childing and such.
I suggest you copy the _BaseShirt, _BasePants, etc to your mod folder(and I would also suggest getting some further structuring going on in your mod folder, but that’s just an opinion) then reparent your BP’s to the new _Base’s in your mod folder.
Also, you don’t overtly go into detail about what exactly it is you’re modifying, especially in regards to changing the skeletal meshes, there are a lot of settings/variables in the Actor Class Attachment Info’s.
-WM