Yes, U can. Try it :
if (!empty($options->post_threads)) {
if ($visitor['user_id'] && $visitor['message_count'] < $options->num_posts_threads && in_array($forum['node_id'], $threadsfids) && !$visitor['is_admin']) {
$this->responseError($options->threads_error);
return parent::actionCreateThread();
}
}
return parent::actionCreateThread();