You don't want to leave the vanilla script. That kills him. You need to replace that script with your own that does all the stuff the vanilla script does and then modifies it to get the result you want.
Yes, to add static cameras you will need to edit the module's GIT. Which means that they won't take effect in a saved game (unless you extract the save and edit its module GIT).
Alternatively, you can create an animated camera, which is a motion track stored in a model that the game can attach a camera to. Any time you see a cutscene with a camera panning or the like, that's an anicam. But you can also use it for simple position switches where you just jump the camera to different points as needed. This would require the use of Blender or 3DS Max and their appropriate I/O scripts.