I have a suggestion that I think would work really well in LBP3. I've had this idea for a while way back in LBP2, but I never came around to sharing it. Simply put, I think LBP3 should have a Sticker Placer and a Material Changer added in it.
Now, when I say material changer, I mean a tool that can change a material using logic. You would place it on a material that you want to be changed, hook it up to a button ( or another input ),  tweak it so it changes it to another material, and boom! You can change the material using a simple input!
Sticker placer - This would work somewhat like an emitter, however it places stickers instead of objects. Now, you could just place some stickers on a sticker panel and hook it up, but sticker panel can be a bit wonky, considering it's an actual material. If you had a sticker placer however, it would place a sticker directly on a material and give it the same effect.

Hmm. The material change is actually a very good idea. Instead of having to do complex emitting work that would be better.
As for the sticker placer, not to sure.