Re: How?
It won't be a retrofit (a bit tough to do for a satellite in orbit, at least now the shuttle's are museum displays), but I'd imagine it'll be lowering the pressure in the main tank as much as they can, overriding some interlocks and forcing a valve or three open to create a path for the flow between the tanks, presumably via pipework that isn't normally supposed to be open via that route/condition.
But it's also wonderful to see yet another piece of space hardware far outliving its designed lifetime, although the cynic in me does have to wonder if they are applying Mr Scott's principle on their lifetime estimates...