I am not familiar with the decals you are referring to. However, a couple of years ago I purchased a set of Mosrite/Ventures model waterslide decals off eBay. I used them on a 1966 Ventures model that I restored. I refinished the guitar back to it's original sunburst finish. After spraying the black color on the face of the headstock, I applied the decal, then I sprayed several layers of clear coat until the decal was flush with the surface. It was necessary to wet sand the clear coats periodically to level out the edges of the decal so that it appeared very close to the original silk screened decal originally on the guitar.
Also I should mention that before placing the decal into water to slide it off the paper, I sprayed a very light coat of clear lacquer on it so that it wouldn't separate when placed into the water.
I think, but not sure, that the most recent decals offered on eBay are a clear Mylar with and adhesive backing. I have not used this type of decal, but I would imagine it would require the same process of spraying clear coats over it's surface once applied to the headstock. My only concern would be that, spraying a clear nitrocellulose lacquer over a Mylar decal may attack the material and deform it, ruining the decal. So it ,might be best to apply the decal and forego any clear over coats.
Here's the one I did.
