The openreach modem is part of the service, and ownership and responsibility for replacing it if it breaks, or your dog eats it should be laid out in your Terms and Conditions with the retail provider.
The LAN2 port is not active, and the device as supplied is only intended for connecting a router to provide the service. You can hack the device, but then if you break it, a small possibility that Openreach might charge you for a new modem.
If you are wanting to experiment, then buy a spare device and use that for the experiments.