您可以使用wp_insert_comment 检测何时向帖子添加新评论的操作。然后在您的操作回调中，您可以使用get_comments_number(), 并使用wp_set_object_terms().

沿着这些路线，

add_filter(
    \'wp_insert_comment\',
    function($id, $comment) {
        if ( (int) $comment->comment_approved ) {
            $post_id = (int) $comment->comment_post_ID;
            $post_comment_count = get_comments_number(
                $post_id
            );

            if ( $post_comment_count > 3 ) {
                wp_set_object_terms(
                    $post_id, 
                    array(\'3-comments\'), 
                    \'category\', 
                    false // don\'t append, overwrite terms
                );
            } else if ( $post_comment_count === 2 ) {
                wp_set_object_terms(
                    $post_id, 
                    array(\'2-comments\'), 
                    \'category\', 
                    false // don\'t append, overwrite terms
                );
            } else {
                wp_set_object_terms(
                    $post_id, 
                    array(\'1-comment\'), 
                    \'category\', 
                    false // don\'t append, overwrite terms
                );
            }
        }
    },
    10,
    2
);