修改 wp-includes/comment-template.php

//去掉用户名
	// For comment authors who are the author of the post
	if ( $post = get_post($post_id) ) {
		if ( $comment->user_id === $post->post_author ) {
			$classes[] = 'bypostauthor';
		}
	}

//添加placeholder
$fields   =  array(
    'author'  => '<p class="comment-form-author">' . '<label for="author">' . __( 'Name' ) . ( $req ? ' <span class="required">*</span>' : '' ) . '</label> ' .
           '<input id="author" name="author" type="text" placeholder="(required)" value="' . esc_attr( $commenter['comment_author'] ) . '" size="30" maxlength="245"' . $html_req . ' /></p>',
    'email'   => '<p class="comment-form-email"><label for="email">' . __( 'Email' ) . ( $req ? ' <span class="required">*</span>' : '' ) . '</label> ' .
           '<input id="email" name="email" ' . ( $html5 ? 'type="email"' : 'type="text"' ) . ' placeholder="(required, never be published)" value="' . esc_attr( $commenter['comment_author_email'] ) . '" size="30" maxlength="100" aria-describedby="email-notes"' . $html_req . ' /></p>',
    'url'     => '<p class="comment-form-url"><label for="url">' . __( 'Website' ) . '</label> ' .
           '<input id="url" name="url" ' . ( $html5 ? 'type="url"' : 'type="text"' ) . ' value="' . esc_attr( $commenter['comment_author_url'] ) . '" size="30" maxlength="200" /></p>',