Back when I was a dumb kid decades ago, I had gotten as far as getting paste wax put on my car, then got distracted and it all dried. It was white and hard as a rock not to mention impossible to get off. So I asked an older gentleman how to remove the dried wax. The answer was to apply a fresh coat of wax over the dried wax and wipe it off before it dries. Son of a Gun....it worked.
Now down side to the wax on the decals is that it may have dried out the decals over time. If this is the case it is a whole different matter to deal with.
Good Luck
2013 Wildcat 353LS (on of the few out there)
2013 Ford SHO
2013 F350 FX4 CC PSD
Good Sam Roadside Assistance (it's a good thing to have):B