Hey @Vollgaser!
So there might be a way to do this but I am unaware of a way to “bake” decals. What you CAN do is have the thing that moves set to “Receive Decals” → false. It should be in the details window. So for instance, on a character, it would be in the details panel of the skeletal mesh specifically. You would disable this on anything that might accidentally move into the decal space.
I want to say there’s a way to set a decal to only project onto static meshes as well… but I’m not seeing that anywhere in the documentation.