But in contract law, a deal is a deal, done on the day it is consumated, i.e. when it's paid for. And the deal is not supposed to be changed unilaterally after that date.

And incidentally, any clause in a contract that would purport to allow one party to change the contract unilaterally would be deemed to be invalid in a court of law.

This brings us back for instance to flight passes, upgrades and J-2 availability which AC tried to change retroactively. One is not supposed to do these things. Even if the tariffs and/or aeroplan rules would state that they can change retroactively, such statements would be declared void in court and I would trust AC's lawyers to be quite aware of that. So, in effect, they are simply an attempt at intimidation. And yes, this is a game that lawyers do understant.