Sorry, [MENTION=13606]Globaliser[/MENTION] - I should have been clearer. The trip is NCL-LHR-BOS and return. Both cancellations and rebookings apply to the return journey: the one in December affected the LHR-NCL leg; the one yesterday the BOS-LHR leg.

As far as I know, I haven’t actively accepted anything from the first change - I did log into MMB, but I don’t think I even selected a seat on the newly rebooked flight. But I know that often (eg mobile phones), you are deemed to have “accepted” a change in contract if you don’t reply or actively do something within a set time period.