The logical thing to do here would be to change the current torch object (item 50) to the lantern object. All current torches become lanterns. Change the current recipe to make item 50, now lanterns. Now add a new item (# ) to be the new torches since they will require special coding anyhow.
From that you will not have to replace all your torches in the current system. If you are smart you will stockpile a crapload of easy to make torches now so you have a ton of lanterns when the system flips over.
If Notch doesn't do that, we can all laugh mightily as people burn down their wooden houses when they mis-click trying to relight the torches.