Child php file for WordPress wp-includes file?

Hi guys,

I have a child theme of Thematic that I’m using, but I’d like a child theme version of a file located in wp-includes (which is at wordpress/wp-includes/comment-template.php). I can make modifications to the file and see the changes required on screen, but I know if I do that and later allow updates to WordPress, it will overwrite the file. I don’t know how to create a child version of it, though, because it is not located in wp-content/themes/thematic – help?