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Can I connect a POTS cable over a cat6a cable

I currently have a UK Master socket which splits into 2 circuits 4 wire for phone extensions and AB line for RJ11 ADSL2 modems.
I can run POTS extensions from the socket, but I need to extend the AB line too. Can I place a cat6a shielded pairs cable with sockets by the master socket and jumper the AB line so I can connect a modem at the other end and would only be using 2 wires currently but will have the extension ready for FTTN.