Why are you wanting to change a master socket with a slave!?
The Master socket is needed, you must have a Master socket.
Do you have more than one master socket?
If so then you must keep the BT (Openreach) socket in place and then yes you can replace any other masters for slaves and you should do this as you should only ever have one Master on a system.
If your BT NTE5 Master socket is damaged, tied or faulty then BT will replace it for you free of charge.
Given that you believe that you have to do something with your phone system i'm assuming that you are experiencing a problem, what is the problem your having?
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