Not really, but you need special equipment (not easily done for home-printed decals).
Blank decal paper used by the decal manufacturers is just paper coated with a thin layer of water soluble adhesive.
The clear film is just another liquid "color" layer applied to the blank decal paper. If the decals are done using silk-screening process (what Microscale uses) the clear areas are applied first, before the subsequent printings of color inks.
I guess nowadays there are probably decal producers using some sort of ink jet printing which can also print clear film before the colors get printed.
