They're called contronyms, and a dictionary that doesn't include them also loses credibility by virtue of being incomplete. While I thought they were inevitable given English's insatiable urge to incorporate any language it can, it turns out other languages have them, too. (I'm obligated to call out biweekly, which isn't a real contronym, but still ends up confusing no matter the context in which it is used.)
That said, we all know that if there will be any consensus on supplying Earth's natural satellite with a new name, it will be "Moony McMoonface."
But these issues apply to the planets that you're not redefining, too?
Too bad no one objected to calling the outer planets Space Balls... I recently realized that I missed the opportunity to suggest calling them Planen'ts.