Spraying with Nitrogen would add ZERO health risk since most of the air around us is already Nitrogen it would simply mix with the air and would not pool up in high or low places. The only danger would be displacing the Oxygen but this would not be a problem either because the paint area would have to be ventilated, if it is not then the paint over-spray would reach toxic (and blinding) levels long before the Oxygen depletion became a problem. The more I think about this the more practical it seems if someone just needs to do just one job and has only a tiny compressor, it would be kind of like a giant rattle can
. Maybe the Cryo tanks would be a bit of over-kill however two or more pressure tanks connected by a manifold (these are available) and using a regulator capable of enough flow this should work and would eliminate the need for a high volume compressor plus it would provide very clean and dry propellant.