我会尝试“wp\\u insert\\u post\\u data”过滤器。

add_filter(\'wp_insert_post_data\', \'new_content\' );
function new_content($content) {    
    preg_match_all(\'~<a.*>~isU\',$content["post_content"],$matches);
    for ( $i = 0; $i <= sizeof($matches[0]); $i++){

        if ( !preg_match( \'~nofollow~is\',$matches[0][$i]) ){
            $result = trim($matches[0][$i],">");
            $result .= \' rel="nofollow">\';
            $content[\'post_content\'] = str_replace($matches[0][$i], $result, $content[\'post_content\']);
        }

    }

    return $content;
}