If you monkey with the socket and it causes damage, then not only the cost of any equipment damaged (regardless of where it is) but the engineer's time in sorting it could find itself to your door. It is breaking your contract with BT to mess with the master socket (other than plugging type-approved stuff into the user section), so IF you come unstuck, you're risking a big bill.
It's not likely that anyone with an ounce of common sense and the foresight to do a bit of research will come unstuck, but it's a risk you run. Yeah, keeping the original master socket to revert to it might cover you, provided you get enough warning of an engineer's visit to put it back. But you may not even know of problems you've caused until the engineer knocks.