I think that would be a stretch. If it was deemed as a voluntary change (which it won't be if your flight is cancelled) then you can do it for a year from the original date, or 355 days from now in practical terms. Involuntary changes are within 1 year of issue date, however. If the ticket has a shorthaul connection then there are games you can play around this. When the customer guidelines eventually emerge then I would expect it to only give a 2 weeks wriggle room from the original date. If it's an Avios booking then frankly it's easier to just refund and start again.