Painting the deck with graphite paint yes, blades no. Try and mow only when dry.
Don't mow wet grass and nothing sticks to the blades nor the underside of the deck.
There is an ideal range of moisture in which to cut grass.
Too dry and it doesn't cut cleanly plus you'll get a dust storm in the thin spots.
Too wet and it's a sticky clumpy mess.
Just right and it cuts nicely and the cut ends mulch nicely or get sprayed out evenly.
I can't think of a single reason to paint mower blades.
If you're worried about rusting, which does no harm, wipe them with any oil before putting the mower away.