Oh!! This idea has quite some potential for later development after you've gotten some of your present stories completed (or as a mind-cleanser when you hit a block on them - I can speak from a certain experience, here). I like the bit about changing the twins from Percy-clones to pranksters and I can see where that change would make a major effect on being able to stop Tom.
Author's response
To my mind the fun in this story is Hermione and Luna fighting over him...