The junction box is unlikely to be surplus to requirements if it joins the external wire to an internal wire which goes to your master socket - they have to be joined somehow!
If you do have an NTE5, you can legally run your own extension wiring from it. If you remove the faceplate (held on by 2 screws) you will see the IDC connectors on the back into which you can krone your extension wires, as per the box with "Removeable User Panel" shown in