I get the impression WillLem has just assumed you can customize every graphic for a pack. I'm 99% sure helper graphics cannot be customized, nor can the cursor. I'll check this to make sure, though.
It's intended that a pack can provide custom skill panel graphics, and custom title / menu screen graphics (including background and font). Cursor isn't intended IIRC, though I'm open to whether it should be possible to customize. Clear physics mode graphics are absolutely not, while lemming sprites are the domain of styles rather than packs.