How to maintain changes to comment-template.php

Question

I have made some custom changes to the file wp-includes\comment-template.php. These changes are periodically lost and I assume it's related to updates for WordPress and the file is modified/re-written.

I have changed:

$comments_link = get_permalink( $post_id ) . '#comments';

To:

$comments_link = get_permalink( $post_id ) . '#disqus_thread';

Is there a way I can persist these changes so they are not lost? Or perhaps there is a better way to make these changes?

Edit

I've tried this code in my themes functions.php file.

function custom_comments_link($comments_link, $post_id){
    return get_permalink($post_id) . '#disqus_thread';
}
add_filter('get_comments_link', 'custom_comments_link', 10, 2);

Answer 1

There's a filter for that: get_comments_link. Refer to source:

return apply_filters( 'get_comments_link', $comments_link, $post_id );

In an appropriate place (such as a site functionality Plugin), just add a filter via callback:

function wpse123906_filter_comments_link( $comments_link, $post_id ) {
    // Return your custom link
    return get_permalink( $post_id ) . '#disqus_thread';
}
add_filter( 'get_comments_link', 'wpse123906_filter_comments_link', 10, 2 );