I found procedure gatewayTransportInit(), it works great. However, I cannot find a procedure that will enable detection of a network connection at level mysensors. I noticed that disconnecting the network plug or resetting the W5500 (37 pin to ground) changes the device's IP address to 0.0.0.0 - then I call gatewayTransportInit() - but mysensor's library must have such procedures - please tell me how to diagnose ethernet connection.
Just for completeness: the right way to do this is to add the json under ~/.platformio/boards and the other files as described in https://community.platformio.org/t/how-use-a-same-chip-but-with-different-environment/18082/4