I had this question when I was getting my PIC endorsement. I didn’t need to renew F/F for the endorsement, I already had advanced F/F and submitted it for an AB ticket way back when. An upgrade may well be a different matter…although I don’t see why.
I’m hearing the new STCW rules are going to require F/F renewals every 5 years from our Compliance Dept. I hope they’re wrong.