That's a pretty interesting idea, though one I've never heard nor considered myself. Though I suppose I was about 14 when I read Ender's Game.
I don't think he should, but I do agree it's his book so he can do what he like with it. At the end of the day, it's a very successful, enjoyable and interesting book to read and the text itself wouldn't be improved one jot by rewriting it as some Mormon propaganda.