所有permalink输出都有可用于修改的过滤器：post_link, post_type_link, page_link, tag_link, category_link, term_link.

一个简单的示例page_link:

function wpd_append_query_string( $url, $id ) {
    // check some condition and add a query string var
    if( some_condition ) {
        $url = add_query_arg( \'var\', 1, $url );
    }
    return $url;
}
add_filter( \'page_link\', \'wpd_append_query_string\', 10, 2 );