I want to add some code to the image attachment page. Normally, I would just duplicate the single.php page as attachment.php and add my new code, but I'm wondering if the attachment pages can be modified using the templates in the theme options? And if so, how do I even go about that?

Thanks!

Try dashboard > appearance > mz options > main templates > image.php.

If it was a snake, it would have bit me. Thanks!