Thanks for the method. I’ve written up detailed instructions for it at https://apple.stackexchange.com/a/382603/21473 https://apple.stackexchange.com/a/382603/2

Thanks for the method. I’ve written up detailed instructions for it at https://apple.stackexchange.com/a/382603/21473 https://apple.stackexchange.com/a/382603/21473. As you can see in that answer, I found a better method to assign the keyboard shortcut. Assigning the shortcut within App Shortcuts instead of Services lets you use the normal ⌘C shortcut in Books while not affecting copying in other apps.