def addToDefinition(self, json_dict):
        """
           The addToDefinition operation supports adding a definition
           property to a hosted feature service. The result of this
           operation is a response indicating success or failure with error
           code and description.

           This function will allow users to change add additional values
           to an already published service.

           Input:
              json_dict - part to add to host service.  The part format can
                          be derived from the asDictionary property.  For
                          layer level modifications, run updates on each
                          individual feature service layer object.
           Output:
              JSON message as dictionary
        """
        params = {
            "f" : "json",
            "addToDefinition" : json.dumps(json_dict),
            "async" : False
        }
        uURL = self._url + "/addToDefinition"
        res = self._post(url=uURL, param_dict=params,
                             securityHandler=self._securityHandler,
                             proxy_port=self._proxy_port,
                             proxy_url=self._proxy_url)
        self.refresh()
        return res