The hallway sits in the middle between the lounge and the dining room where he has the computer, so it should be pretty easy to obtain a stable wifi connection and to me it would make sense eliminating the wiring going into the lounge.

LOL
In conjunction with your reply to me that there isn't even a proper socket in the lounge, everything probably becomes much simpler. I'm assuming the computer already connects wirelessly?
*** Beware - read my reply where you suggest the master may be in the garage. ***
You simply open up that hall socket, and if it does have that capacitor all is well. You simply disconnect the wire that goes to the lounge and connect the router using the dangly filter in the hall. With one caveat, it obviously needs a mains supply.
I don't know much about freesat though. You imply in your opening post that it needs an internet connection as well as its satellite dish, and that it can have a wireless connection to your router.
If so, then go for that setup! Forget the faceplate worries, and forget the instability worries. There is nothing to worry about unless Dad wants to get rid of the dangly filter in the hall.
Except! Where is/are the phones? Are they old-style needing a phone socket, or a modern DECT system just needing a socket for the base station?
My broadband basic info/help site -
www.robertos.me.uk. Domains, site and mail hosting -
Tsohost.
Connection - AAISP Home::1 80/20. 200GB. Sync 71097/14070Kbps @ 600m. BQMs -
IPv4 &
IPv6
Edited by RobertoS (Sat 31-Mar-18 19:45:41)