Alter Webform email body

I’m unable to find an example of altering the body of the Webform email confirmation according to the value submitted.
I’ve got in my form a select field, I would like to change the body of the email according to the selected value (not only include the value in the body but change completely the message).

I have thought about something like this but not sure if it works (unable to test at the moment, sorry):

 if (isset($message['params']['email']['eid']) && $message['params']['email']['eid'] != 1) {
      if ($message['params']['submission']->data[1][0] == 'company') {
        $message['body'][0] = 'Thank you .. bla bla.
        Bla bla bla.
        ';
      }
    }

Or is it possible to do in form_alter hook or maybe some module ?

/**
 * Implements hook_mail_alter().
 */
function YOURMODULENAME_mail_alter(&$message) {
  // Check here for your mail key
  if ($message['id'] == 'modulename_messagekey') {
    $message['body'][] = 'Thank you .. bla bla.
        Bla bla bla.
        ';;
  }
}