def change_custom_svc_var(self, service, varname, varvalue):
        """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
        """
        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())