Yes, I understand what do you mean. As you may see in the inc/classes/BxDolEmailTemplates.php file the replacement keys are defined in the PHP code as an example here:

* @section example Example of usage

 *

 * Send an email using email templates:

 *

 * @code

 *

 *     // define custom template variables

 *     $aPlus = array();

 *     $aPlus['email'] = 'ktoto@example.com';

 *     $aPlus['conf_code'] = '123456';

 *     $aPlus['conf_link'] = BX_DOL_URL_ROOT . 'page.php?i=confirm-email&code=123456';

 *     $aPlus['conf_form_link'] = BX_DOL_URL_ROOT . 'page.php?i=confirm-email';

 *

 *     $aTemplate = BxDolEmailTemplates::getInstance()->parseTemplate('t_Confirmation', $aPlus); // get class instance and parse template

 *

 *     if ($aTemplate && sendMail('ktoto@example.com', $aTemplate['Subject'], $aTemplate['Body'])) // send email if template exists

 *         echo 'email was successfully sent';

 *     else

 *         echo 'email send failed';

 *

 * @endcode

 So new "terms" like your new field should be added in the PHP code only.