Can I modify the camera path, the galaxy, etc.?
No, you can’t. The package contains the prerendered footage (1500frame 3840×2160 px resolution galactic fly-through render), the After Effects CS 5.5 project file for expanding this prerender (this project file contains the camera path and reference objects from the original scene – which are not included – and also contains some customization example).
So you can get more than a conventional stock footage, but you cannot create a custom camera path.
If you need a custom trajectory please contact me through my profile page.