How can I create a new imovie theme (or customize an existing one)?
The themes are stored within the Application bundle itself, which is code signed, so even if you figure out how to modify them - the OS will not want to run the tampered application.

You might be better off with the Pro Version of the tool if you need to customize a theme and control or you might be able to create the title and end sequences in Motion and use iMovie for the rest of the editing. That's far less expensive than the Final Cut Pro price - but you can test drive that for free if you wish.


https://www.apple.com/final-cut-pro/