Re-routing phone line and replacing master socket

[#1]

Hi,
I hope someone can help, as after all my searching I've read some conflicting advice regarding re-routing of a phone line that we're soon to need.
The house has a couple of old, wooden sash windows that we're looking at replacing with modern double-glazed units.  However, one of the windows has the phone line routed through the sill, as you can hopefully see in the photos attached.  This then joins onto an ancient sort of junction box, that I'm fairly sure is tightly packed with dead spiders and other relics.
So the plan would be to get the phone line rerouted into the house via an alternative route (alongside existing cabling, probably) and a new master socket installed.  As far as I understand, the external wiring is the responsibility of BT/Openreach, and the master socket seems to have to be dealt with through the service provider.  Or maybe it all has to be done through the service provider - the Openreach site seems to suggest so!
Is this the case here?  Will we have to get BT to reroute the phone line, then separately get Plusnet to schedule the master socket move?
Cheers! 

[#2]

If an Openreach visit is required to get your line activated then they should have no problem rerouting the cable and they will be replacing the master socket with a modern one.
Depending on the location that the new master socket is required the engineer may be required to splice some new cable externally to extend existing cable but they shouldn't have any issues doing this.
However I'm assuming that the line you have is already active? then the above should still apply but you will have to request line rerouting or master socket relocation.

[#3]

Yeah, sorry, forgot to mention - the line is already active and working fine!  So we would request the rerouting through Plusnet, is that right?

[#4]

Yes that's correct.

[#5]

If the line is active you will have to request via Plusnet that the socket be relocated by BT Openreach, there is a fee of £160 attached to this work.
I have just been asking about this as when (before my time) BT installed the master socket here they did so up against the window frame in a 2' deep window sill, which is the coldest spot you could pick and the master socket only lasts 9-12 months...