A single swipe of MEK over a decal that already has future or flat varnish over it and has silvered. DO NOT TOUCH UNTIL COMPLETELY DRY. (Tony gave me this one and I used a lot on the Pencil). MEK melts almost anything including paint and plastic, so use sparingly. Flat over decal once it settles.
Also, to get Roden Decals to go down, test with acetone mixed with water - again single swipe until dry, then go again.