Could you?
I treat free will as an assumption:
- If we are, in fact, predestined, assuming I have free will doesn't hurt or matter.
- If we do have free will, I'm applying that free will to make decisions based on a correct assumption
- If we do have free will and I had assumed we were predestined, this could have worse results. At the very least, it is unlikely to improve outcomes
Not to mention you were predestined to assume so.