With reference to Kevin Lim's and Steven Gradi's letter , I would suggest that Astro may have no legal basis for upgrading their subscription to the Emperor package.
In essence, what Astro is doing is varying the terms of its service contract with its subscribers. Under contract law, this cannot be done without the consent of the subscribers.
What's more, a subscriber's silence cannot equate to consent unless the subscriber, after the actual upgrade continues to receive the benefit of the upgrade and act in a way consistent to an acceptance of the upgrade.
Otherwise, Astro would not be able to enforce their purported upgrade just because their subscribers have failed to notify them.
The only other exception to that rule would be if Astro has the right under its service contract to upgrade or downgrade subscribers without their consent. I doubt this is the case.