вместо
$this->db->query("INSERT INTO " . DB_PREFIX . "customer (identity, firstname, lastname, email, telephone, fax, newsletter, customer_group_id, password, status, date_added) VALUES ('" . $this->db->escape($data['identity']) . "', '" . $this->db->escape($data['firstname']) . "', '" . $this->db->escape($data['lastname']) . "', '" . $this->db->escape($data['email']) . "', '', '', '0', '" . (int)$data['customer_group_id'] . "', '" . $this->db->escape(md5($data['password'])) . "', '1', NOW())");
сделай
$this->db->query("INSERT INTO " . DB_PREFIX . "customer (identity, firstname, lastname, email, telephone, fax, newsletter, customer_group_id, password, status, date_added, approved) VALUES ('" . $this->db->escape($data['identity']) . "', '" . $this->db->escape($data['firstname']) . "', '" . $this->db->escape($data['lastname']) . "', '" . $this->db->escape($data['email']) . "', '', '', '0', '" . (int)$data['customer_group_id'] . "', '" . $this->db->escape(md5($data['password'])) . "', '1', NOW(), '1')");
не проверял, но должно работать..
если включишь модуль он появится в слева или справа в виде модуля авторизации, так что не страшно