下面是一个示例代码，可以帮助您入门-基本上它会拦截用户提交的帖子插件创建的新帖子（至少它会尝试，但一般来说，在该请求期间不应该创建任何其他帖子）。如果已经存在具有该名称的帖子，我们会将内容作为评论添加到该帖子，并重定向到该评论的URL，否则所有其他内容都由插件本身决定。

// Hook to the "wp_insert_post_empty_content" filter, since that is the only place
// we can intercept the creation of a new post and not let it be created
add_filter( \'wp_insert_post_empty_content\', \'intercept_user_submitted_post\', 10, 2 );
function intercept_user_submitted_post( $maybe_empty, $post_data ) {
    if ( isset( $_POST[\'user-submitted-post\'] ) && ! empty( $_POST[\'user-submitted-post\'] ) ) {
        $target_post = get_page_by_title( $post_data[\'post_title\'], OBJECT, \'post\' );

        // We found an existing post!
        if ( $target_post && $target_post->ID ) {
            global $usp_options;

            if ( stripslashes( $_POST[\'user-submitted-name\'] ) && ! empty( $_POST[\'user-submitted-name\'] ) ) {
                $author_submit = stripslashes( $_POST[\'user-submitted-name\'] );
                $author_info = get_user_by( \'login\', $author_submit );

                if ( $author_info ) {
                    $authorID = $author_info->ID;
                    $authorName = $author_submit;
                    $authorEmail = $author_info->user_email;
                } else {
                    $authorID = $usp_options[\'author\'];
                    $authorName = $author_submit;
                    $user_data = get_userdata( intval( $authorID ) );
                    $authorEmail = \'\';
                }
            } else {
                $authorID = $usp_options[\'author\'];
                $authorName = get_the_author_meta( \'display_name\', $authorID );
                $user_data = get_userdata( intval( $authorID ) );
                $authorEmail = $user_data->user_email;
            }
            $authorUrl = stripslashes( $_POST[\'user-submitted-url\'] );

            $time = current_time(\'mysql\');
            $data = array(
                \'comment_post_ID\' => $target_post->ID,
                \'comment_author\' => $authorName,
                \'comment_author_email\' => $authorEmail,
                \'comment_author_url\' => $authorUrl,
                \'comment_content\' => $post_data[\'post_content\'],
                \'comment_type\' => \'\',
                \'comment_parent\' => 0,
                \'user_id\' => $authorID,
                \'comment_author_IP\' => preg_replace( \'/[^0-9a-fA-F:., ]/\', \'\',$_SERVER[\'REMOTE_ADDR\'] ),
                \'comment_agent\' => isset( $_SERVER[\'HTTP_USER_AGENT\'] ) ? substr( $_SERVER[\'HTTP_USER_AGENT\'], 0, 254 ) : \'\',
                \'comment_date\' => $time,
                \'comment_approved\' => 1,
            );

            $comment_id = wp_insert_comment( $data );

            // Redirect to the comment URL
            wp_redirect( get_comment_link( $comment_id ) );
            exit;
        }
    }

    return $maybe_empty;
}

PS：该代码还有更大的改进空间，比如在用户被重定向时显示消息，或者在评论中添加照片，但我将由您决定。我认为上面的代码是一个很好的起点。