Yes. Putting in additional tiles, character or updating the previous static tile to be animated. That kind of things.
That's what I meant: if you update a static tile, that's all good and well. But the people that already downloaded it an put it in a game, might have used for a static purpose. If you exchange that static tile with an animate one, you might break design - if the developer propagates the update into the game.
Putting additional things into a pack should not be a problem.