Also, as far as magic: There's some precedent in Thor's corner of the universe for magic shifting and changing. Loki mentions that dying and being reborn was one way to free himself from his own evil impulses because he, as a creature of magic, basically exists as a narrative. Change the story, change the person. Something similar may be happening with Mjolnir. Odin may have enchanted Mjolnir initially, but Thor and his actions have raised Mjolnir's profile to such an extent that its magic may be outgrowing and becoming even more powerful than Odin. Remember, the God Butcher arcs of Jason Aaron's previous series basically put forth the idea that Thor is literally the greatest god who ever lived in the entire universe.