One thing to remember is that if you take a pressurized gas and release it, the gas will be very cold. I'm not sure exactly what would happen, but I don't think the reducers would react well to sub-zero temperatures. It is entirely possible that the cold spray will take moisture out of the air and freeze it into your paint. Ice crystals in the paint would not be good. Paints are designed to be used with compressed (and therefore warm/hot air). I don't think cold nitrogen will work well.
81 Grand Prix, 355, 700r4, 8.5" 4.10
64 Oldsmobile Jetstar, all original