why not just lining paper and paint it? then, when you want it back you just need to strip the paper. provided you are careful when stripping and use a fairly weak mix of wallpaper paste you should have no problem.
when we moved into our house we stripped the walls in one bedroom to find a humpty dumpty mural (done badly) beneath. we covered it up again but the wallpaper came away leaving the mural completely intact. still there now though it's never likely to see the light of day again!
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