I had the same thing happen when I made a pre-emptive Superbowl reservations hoping the Ravens would repeat and play at Metlife Stadium. (big mistake) The property emailed me and said very similarly that they were changing the cancelation etc etc etc. and that I needed to acknowledge the changes or my reservation would be canceled.

I called MR and told them of the email. They called the property and spoke to GM who sent email. He got his butt handed to him. My terms at time of reservation were continued. I canceled when Ravens were eliminated.

If I were you, i would contact Marriott to document and make sure your reservation isn't impacted.