Clay bar would have probably worked fine for removing the wax too. I don't think you'd want to use clay on the decals, but that questions probably better asked of Rider Graphix. They suggest not waxing the matte finish decals though.
2012 Mustang GT/CS Race Red
Mods: Boss 302 Manifold, JLT Carbon CAI, Corsa Sport Axle-back Exhaust, 3.73 Gears, Barton Shifter & Bracket, JLT Oil Separator, Hood Struts, Hood Spears
1987 Mustang GT - Dove Grey, T-Tops, loaded... RIP