Anyway to add decals to the Paint tool?

So I’ve been fussing over the Paint tool. Is it possible to add in decals to the Tool? I’ve been needed to use the advanced blood stains which are absent from the regular list. I’ve found the files I want to add, but I can’t find where the list of the current decals are so I can add in the new ones. Anyone know where it is, or whether I can actually do this?