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