My NPD ex is all over the place, and if I ask anything of him he's an emotional wild card. Guess what? So is our teenager! He is sympathetic to me when he's with me and sympathetic to his dad when he's with his dad. He's cranky with his dad to me, and cranky with me to his dad.
I wouldn't think too much of it. This is the reality of the teenager that changes households.
I recently posted about a crisis I had with him and his insistence that he live with his dad, and my feelings of just not knowing what to do or if I had to fight or if I had the fight in me. I figured it out, and it amounted to him just needing some safe mom time after a long summer with his dad. Anyway.
I don't understand how he went from being agreeable, to forgetting about all of our previous discussions, and changing the rules on me.
Accept and move on. He will probably change the rules on you. He will blame you and turn the tables on you. Accept it, plan for it, and be glad if it doesn't happen, but it's what he'll do.