Decals (and texture images) should be a permanent part of the model, not dependent on a particular users customization environment.
Decals are a valuable to leverage the model to communicate information. They are great for showing warning labels and other complex pictorial information that make the experience so much more meaningful. The current system limits this usefulness to the superusers, and a somewhat fragile system prone to breakage.
Currently image file decals are stored in the \SDUserCustomizeDir\Rendering file in a cryptic manner, so for most users the only person that can see the decal is the creator. Someone that is well versed is able to move the .lwa to the Site or Corp customize dir, but must continue migrating this forward if they use SDVERSIONDEPCUSTOMIZEDIRS. Then if you want to send a package file out someone outside the system they can't see the decal.