For a Four Seasons, an FSPP travel agent is likely a better choice.
I did exactly this with a reservation earlier this year. I did initially book directly with Four Seasons, but with some email and a quick phone call, got it transferred to DavidO's agency to make it a FSPP booking. I don't know if the FSPP thing, or the specific agent made a difference, but we got a large upgrade and were treated very well during our stay, so it's certainly worth making the change if the current booking allows it.