They'll just mess about with the cover of your master socket. Mine came and went in 45 minutes 🙂
Hi and welcome to the forum,
Do you only have the one socket? and are there 2 power sockets nearby?
I have attached a sketch to show how thing are arranged - this is not a BT approved drawing - just how I believe things are wired - hope it gives you a clue as to what goes where.
As an extension to this question - Must the 30 meter extension wire be installed indoors or can it be routed around the outside of the property?
It can be external if the engineer feels its better or easier to do this way.
I had an old style phone socket (not a modern NTE5). The Infinity installer replaced the WHOLE socket and installed an NTE5 with Infinity face plate.
If the OP has one socket then, unless he asks for an extension, it will either just get a new faceplate in its current position, or a new NTE5 with faceplate will be installed in the same position using the existing cable.
Both the phone and the Openreach VDSL modem plug into the same faceplate (it has two sockets in it).