I want all new books I'm adding in Pelagiad Expanded to be compatible with the Book Rotate mod. So I need to add a script to each new book but I don't know if I'm supposed to take the script directly from Book Rotate or not. I want it to be so that people who don't use Book Rotate won't have any problems with the books and for those that do use Book Rotate, they'll be fully functional with it.

Take the script(s), but rename them. Note that the scripts do use a global variable. You can use that variable with its current name so you don't have to change it in every script, but you must make sure that its value is the same in your mod as it is in the BR mod; otherwise none of the scripts will work.