As the OP - can I just ask, as a non railway chap but with loads of experience in scheduling Shift and Irregular Hour Workers in another industry - what makes Kings Cross so difficult.
As I see it drivers are asked to drive from Finsbury Park to Kings Cross instead of Moorgate - so no tunnels, no other stations and less driving time.
Now dealing with 'signing routes' - sorry if that's the wrong term - I appreciate this necessity.
However the route from Finsbury Park to Kings Cross has been completely revamped for all trains into Kings Cross.
Has every driver from no matter where had to re-sign the route since the Kings Cross revamp - really?
From where I sit I'm yet to be convinced, at all, that any current driver into Moorgate isn't competent to drive into Kings Cross.
Or is this just a bit of local branch awkwardness.
In First Capital Connect days there were only 5 driver depots. With the exception of a couple of outlying routes every driver signed all routes and traction on the route, so these problems were mitigated.
Since GTR took over the number of depots have increased, but all depots only really do one or two routes. With the increase of depots the number of drivers also increased. The area has always seen a high turnover of drivers (particularly in the London area) and, as a result, a high proportion of trainees.
As training of new routes and traction has been very difficult on account of social distancing restrictions (which have, to all intents and purposes, only been suspended in the practical sense for drivers for a matter of weeks)
There are several hundred GTR drivers who sign Kings Cross from the north and training even a small proportion of these on a new route (which is quite complicated, AIUI because of the different routings available Finsbury Park to Kings Cross takes several weeks to learn) within the space of a few weeks simply isn’t practical.
In answer to the “would the drivers have to relearn the route if it’s resignalled” question, generally the short answer is yes. To what extent and how long it would take would depend on the extent of the resignalling, but short answer, yes