If crown caps needed to be waxed, they'd have come with wax right along. It's one of those technologies that doesn't really need any help. By the time anything significant makes it in past that seal, any beer in there is probably gone for reasons other than oxygenation.
OTOH, if you just want it to look cool, wax away....... love pulling the wax top off a bottle of Knob Creek.
“Malt does more than Milton can / To justify God’s ways to man”
-A. E. Housman (1859–1936). A Shropshire Lad , 1896.