Add a filter to get_comments_link()

Modifications of the core code are not recommended.

Note that the core get_comments_link() function considers two cases of $hash:

$hash = get_comments_number( $post_id ) ? '#comments' : '#respond';

Also note the second input argument is $post_id.

Here’s your modified example:

add_filter( 'get_comments_link', function( $link, $post_id )
{
    $hash = get_comments_number( $post_id ) ? '#mycomments' : '#myrespond';
    return get_permalink( $post_id ) . $hash;

}, 10, 2 );

or another approach might be a simple replacement:

add_filter( 'get_comments_link', function( $link, $post_id )
{
    return str_replace( 
        ['#comments', '#respond'], 
        ['#mycomments','#myrespond'], 
        $link 
    );

}, 10, 2 );

But it sounds like you want to modify the get_comment_link() according to your line number reference. Then you should consider the get_comment_link filter:

add_filter( 'get_comment_link', function( $link, \WP_Comment $comment )
{
    return str_replace( 
        '#comment-', 
        '#mycomment-', 
        $link 
    );

}, 10, 2 );