code: def install_caller_instruction(self, token_type="Unrestricted",
                                     transaction_id=None):
          
          response = self.install_payment_instruction("MyRole=='Caller';",
                                                      token_type=token_type,
                                                      transaction_id=transaction_id)
          body = response.read()
          if(response.status == 200):
              rs = ResultSet()
              h = handler.XmlHandler(rs, self)
              xml.sax.parseString(body, h)
              caller_token = rs.TokenId
              try:
                  boto.config.save_system_option("FPS", "caller_token",
                                                 caller_token)
              except(IOError):
                  boto.config.save_user_option("FPS", "caller_token",
                                               caller_token)
              return caller_token
          else:
              raise FPSResponseError(response.status, response.reason, body)
docs: Set us up as a caller
          This will install a new caller_token into the FPS section.
          This should really only be called to regenerate the caller token.