It would be better if Guns N' Roses...
...started playing when The Rock slamed the crystal into the hole.
Also, the movie characters would hear it and react to it, like "What is that sound? Where is it coming from? What's going on?"
Additionally, there could be an inner joke where Jack Black says something like "What kind of awful music is that?!" This would even fit with his character of a trendy girl who would never listen to dad rock.
In the real movie the song is wasted for the credits. In my version we would have an awesome scene.
Hollywood, I'm available for hiring.