Hello! I am a newbie to this program. I got the Citi AA card and accrued more than 75k miles. My questions for redeeming OW partner flights:

1. What are the charges for canceling or changing an award flight on partner airlines?

2. What are the sweet spots of this program? I can see some transpacific flights being of affordable (though not the best) value, if there are availabilities.

3. What are the stopover rules?

I have done some research on blogs, but could not find great and recent answers to my questions. I would appreciate your help. Thanks a million!