How often do they change the benefits for APH's? And if they change a benefit to your disadvantage after you buy one, do they honor the original benefit or are they subject to change?
Usually the updates to APs occur once a year. Really I haven't seen any benefits changes to my AP. If they do change they would go into affect when you renew your pass.
The benefits are valid for a calendar year. Your benefits are subject to change. However, I don't recall anything ever changing that caused major issues. Mainly it is the changing of blackout dates for the power pass.