I think Tom said that something like this would need a base of "Magic" and that isn't going to happen.
I vaguely recall this, but can't find the exact post on the subject. To clarify, the thought was that if someone cast a Fireball, in theory, someone with Change Fire should be able to modify the spell to become Fireflies before it hits. But like I said, I'm assuming you'd have to create a new modification spell for each and every base. There wouldn't be a catch-all (I think that's where a base "Magic" would come in).
