code: def change_custom_svc_var(self, service, varname, varvalue):
          
          if varname.upper() in service.customs:
              service.modified_attributes |= DICT_MODATTR["MODATTR_CUSTOM_VARIABLE"].value
              service.customs[varname.upper()] = varvalue
              self.send_an_element(service.get_update_status_brok())
docs: Change custom service variable
          Format of the line that triggers function call::
  
          CHANGE_CUSTOM_SVC_VAR;<host_name>;<service_description>;<varname>;<varvalue>
  
          :param service: service to edit
          :type service: alignak.objects.service.Service
          :param varname: variable name to change
          :type varvalue: str
          :param varvalue: variable new value
          :type varname: str
          :return: None