You can exercise free will at any time, thus altering your unfolding path of fate to some extent...however, you can also exercise your free will to declare: "I have no free will." ;-) And no one can stop you from so doing...not God, not Nature, not the laws of physics, nothing. They can stop you from doing it tomorrow by killing you pre-emptively today, but they cannot stop you from exercising your free will in the manner you decide to at the moment you decide to. You free will is merely limited to what is actually possible at the time, and that is all. The notion that a being having free will would argue that he hasn't got it is kind of hilarious, but it just shows how much independence we have! Plenty. We can assert absolutely anything we wish to. And we do.