You should have no problem, Nitrocellulose will rarely effect Poly, but spraying poly over Nitro is usually a wrinked mess. Make sure to prep the headstock with 600 and 800 to smooth, and give the decal a good gripping area. Only do the area of the decal to 800, the rest of the headstock will be fine with 600. Also, I would avoid spraying tinted lacquer over the decal, it will tint the decal, and that doesn't usually come out well. Spray the tinted lacquer first, then scuff to 600 when dry, do your decal and cover the decal with clear.