I've had reasonably good luck downplaying the visible edge on decals this way. It's a little labored but it works most of the time- here are my steps, your mileage may vary:
1. After base color coat but long before any weathering passes, shoot a coat of gloss lacquer. More on why lacquer in a sec.
2. Apply decal using Micro Set, let dry, and hit with Micro Sol (that's why i use Lacquer Clear spray - Micro Sol eats my acrylic clearcoat every dang time. Others may not have experienced this and it could well be my rotten luck, so take that with a grain of salt, but this is what works for me. Humbrol Decal-Cote and Decal-Cote 2 are also great for the job, IMO.)
3. Once that coat cures completely, hit the decal with a lightly-thinned single-pass brush of enamel Clear from the bottle. The enamel clear forms a meniscus at the edge of the decal and obscures the edge of the decal unless you are in a just-so light and are really looking for it.
4. Spray with a matte coat pass. The previous brushstroke of clear gloss should have smoothed the edge enough to make it near-invisible.
Mind you, there are washes and filters happening when all this is going on so this is all part of my little detailing ritual, I don't do all this STRICTLY for the decals, so go with what works best for your method.
**edited** Apparently my brain was saying "lacquer" but my fingers were saying "enamel."