The concept of 'Free Will' is ultimately meaningless from inside the allegedly controlled system. You cannot distinguish whether or not your actions are your own or are dictated by your subconscious/little green men/the Wheel of Fate/giant metal hand in the sky. You would still know that your will is your own, unless you explicitly know that you're being mind controlled by a shadow priest.
An outsider may be able to observe the system's behavior and make a conclusion, whether or not the system is influenced from outside or is completely deterministic, but that would still accomplish nothing. You can't "rebel" against Fate, as that is just a part of it.
More meaninglessness:
1. Universe A is deterministic.
2. Outsider Omega in Universe B observes universe A and reveals that information to the people of Uni-A.
Will it ruin the deterministic nature of Uni-A and free it/destroy it? Or was Outsider Omega always predestined to reveal that information as a part of Uni-A's preset Fate and it isn't possible to defy the machinations of the tyrannous stars?
A time traveler would observe the universe as pre-determined, regardless of whether it is true or not. Any timeline changes originated by the time traveler are predetermined by the meta-Universe and the meta-timeline is forever unchanging. You could keep tossing that coin, but it will never land on its edge, not without outside help.