After the new booking hall opened, the old stairs were blocked off, and now
the only exit is to the northern end of the platforms - e.g. the way out has
moved from one end of the station to the other.

That's not strictly correct: the new entrance is roughly half way along the
platform, but I see the point you are making!

Also, historically, there were actually entrances further along than the old
booking office entrances, used for football matches.

And, even now, there are staircases at the extreme North end of both platforms
(you can see the curved stairs when approaching the station from the North),
which I assume can be used for football matches, but are normally sealed off.

Marc.