Just use a water-proof grease on the bolt and when you do the annual service (that's each year!) it'll come out nice and easy....
Eversieze has copper and nickel in it... You'll just be adding yet more metals to that underwater battery you have.
Chris.............
Sealants have to be used on some stuff though I think they put high temp on the manifold bolts,exhaust tube etc
Good for you, No, it should not be painted, now go get a stainless replacement cap screw bolt, & a new anode. If any doubt of any bolts composition, put a magnet on it.