EUP Additional Slots

I have been working on Custom EUP’s. I know exactly how to put in new uniforms in the default slots and how to add multiple / textures for that slot. My question is, if anyone know how to add multiple slots in a category. For example. My current slot for prop hats will only allow me to see around 12 variations. And id like to add multiple if possible. I have seen some eups have several slots for hats, but only around 12 were visible, if that makes sense. Thanks for any response.