<?php if ( comments_open( $post_id ) ) : ?>
        <?php do_action( 'comment_form_before' ); ?>
        <div id="respond">
            <h3 id="reply-title"><?php comment_form_title( $args['title_reply'], $args['title_reply_to'] ); ?> <small><?php cancel_comment_reply_link( $args['cancel_reply_link'] ); ?></small></h3>
            <?php if ( get_option( 'comment_registration' ) && !is_user_logged_in() ) : ?>

add_filter( 'comment_form_defaults', 'custom_reply_title' );
function custom_reply_title( $defaults ){
  $defaults['title_reply_before'] = '<span id="reply-title" class="h4 comment-reply-title">';
  $defaults['title_reply_after'] = '</span>';
  return $defaults;
}

h4, .h4 {
/* styles */
}

function my_comment_form_before() {
    ob_start();
}
add_action( 'comment_form_before', 'my_comment_form_before' );

function my_comment_form_after() {
    $html = ob_get_clean();
    $html = preg_replace(
        '/<h3 id="reply-title"(.*)>(.*)</h3>/',
        '<p id="reply-title"1>2</p>',
        $html
    );
    echo $html;
}
add_action( 'comment_form_after', 'my_comment_form_after' );

add_filter( 'comment_author_says_text', 'sp_comment_author_says_text' );
function sp_comment_author_says_text() {
    return 'author says';
}


add_filter( 'comment_form_defaults', 'sp_comment_form_defaults' );
function sp_comment_form_defaults( $defaults ) {

    $defaults['title_reply'] = __( 'Leave a Comment' );
    return $defaults;

}