...and that's the procedure that's been in the Thameslink rolling stock spec since it was published, and in all the various NR change notices quoted, so available to me as a member of the public for about two years now.
The problem for me is that every time I've mentioned it, a load of replies have attempted to explain why it won't ever happen. In this thread for instance, your starting point was:
"I have been recently told that the wiring form Farringdon to City Thameslink will never be made live."
and then westcoaster:
"Incorrect change over will always be at farringdon, this has been confirmed to us on numerous occasions..."
As I've said before, why would they spend £millions on this and not use it?