If the existing paint is lacquer then a paper towel damp with lacquer thinner will immediately dull the paint by just swiping the towel across the paint.
If the paint is acrylic enamel without hardener then lacquer thinner will immediately eat into that paint and cause it to lift like you applied paint stripper. If the paint is acrylic enamel WITH hardener then lacquer thinner will normally not have an effect on it. The same can be said of acrylic urethane in single stage or clearcoat. I can lightly sand paint like that and get a small smell of the paint dust and tell you if its acrylic enamel with hardener and just by the smell of the dust I can in most cases tell you what brand of paint it is/was.
If the paint is acrylic enamel with hardener or acrylic urethane single stage or clearcoat there is not much you can spray on top of it that will have a negative reaction to those type of paints (short of spraying on a paint stripper).