Tony,

I wouldn't deflate them, for fear of possibly messing up the balancing.

Two thing you could do to mask them easily.
(1) wipe a thick coat of grease on the tires, and wash them off ith
solvent after painting.
(2) paint a good coat of dish washing soap on the rubber, and let it dry
good, and then pressure wash the tires to remove the paint.

Good Luck,

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Terry--
74 Campmobile- (Clementine)
85 GL- (Delilah)
86 BMW 325 ES- (Eva)