您想尝试以下操作（未经测试）：

// Nofollow in content
$author_id = get_the_author_meta( \'ID\' );
add_filter(\'the_content\', \'my_nofollow\');

function my_nofollow($content) {
    //return stripslashes(wp_rel_nofollow($content));

    return preg_replace_callback(\'/<a[^>]+/\', \'my_nofollow_callback\', $content);
}

function my_nofollow_callback($matches, $author_id) {
    $link = $matches[0];
    $site_link = get_bloginfo(\'url\');
    if ($author_id === 4) {
        if (strpos($link, \'rel\') === false) {
            $link = preg_replace("%(href=\\S(?!$site_link))%i", \'rel="nofollow" $1\', $link);
        } elseif (preg_match("%href=\\S(?!$site_link)%i", $link) && (strpos($link, \'rel\') === false)) {
            $link = preg_replace(\'/rel=\\S(?!nofollow)\\S*/i\', \'rel="nofollow"\', $link);
        }
    }
return $link;
}