Easy methods to add code for wp-comments-post.php over capabilities.php?

I modified the file wp-comments-post.php by including this in there:

setcookie('addcomment', $_SERVER['HTTP_REFERER'], (time()+300), "/");

After 54 traces, ultimately it turned like this.

...nsent Remark creator's consent to retailer cookies.
 */
 
setcookie('addcomment', $_SERVER['HTTP_REFERER'], (time()+300), "/");
 
do_action( 'set_comment_cookies', $remark, $consumer, $cookies_consent );

$location = empt...

Easy methods to do the identical utilizing capabilities.php?

Sorry for my English.