Sure, though you have to shut down the whole line because it's not all overhead electrification, there are sections where tube lines run past and have 3rd rail

Sure, though you have to shut down the whole line because it's not all overhead electrification, there are sections where tube lines run past and have 3rd rail electrification (and may even have been running). The whole lot has to be shut down, you have to get all the people on all the trains to a safe place and then make sure it's safe before turning everything back on. Not saying it's impossible, just that it's not the most straightforward.