Hi Mark,
Once you are happy you have removed all the paint you want to just spray with a good varnish, flat or gloss - your choice, and everything should be fine. Once sealed the hairspray will not react further with water, this is evidenced by the fact you can apply decals with no effect on the paintwork. Good luck and all I would say is, buy an unscented hairspray - unless you want your model area smelling like a hairdressers for days afterwards.
All the best,
Paul