Hi .. the modbus read/write nodes dont accept a msg directly to change the IP configuration
but there is the Modbus Flex Connector node in the same collection that does that.

You can send it a msg like :
msg.payload = { 'connectorType': 'TCP', 'tcpHost': '127.0.0.1', 'tcpPort': '10502', 'unitId': 2 } return msg
I havent used it in a project but i did some tests and you may need some delay before polling
in order to wait for the configuration settings to actually change