“Is it possible to change the ‘Leave a comment’ text to something else that’s personalized to the content of the site?”
It sure is! In your WordPress Admin dashboard, go to Settings > Discussion and scroll right to the bottom of the page. Under the “Comment Form” header, enter new prompt text and click Save Changes.
Update Feb 2017: You may not see this option on the mobile version of WordPress Admin. If so, switch to desktop instead.