I was in a similar situation last week when I was looking to remove my FFP # prior to my flight as I wanted to submit post my membership reset, I discussed the issue with the live CX WhatsApp agent who said I would lose all of my DM seating benefit as I was able to allocate myself to the front 2 rows despite F not being offered on my flight. The agent said if I removed my FFP # then the seat would be reallocated and I would be seated in the business class section. This was communicated the day before my flight and I would not be able to remove it on the day of my flight at anytime.