TexasPT, technically the answer the phone agent gave you is probably correct, however the airport agents have lots of leeway with the rules, esp. if there are empty seats on a plane.

When I took the flight out of MIA instead of FLL, I got the same answer on the phone, but I had first found out that the flight I wanted to take (roughly 2hrs before the FLL flight) had plenty of empty seats. I then went to the airport and asked the Gold or Platinum check agent if I could take that flight. If they had said NO, I would have gone to the gate. If there are empty seats, you should have no problem. Just make sure that you have somebody with you at MIA that is willing to take you to FLL in case it doesn't work.

jAAck, did your partner go to the airport or talk to a phone agent?

BTW, I have done the FLL/MIA switch several times on the outbound leg, but only once on the return.

Neil