But in this example Omega has already selected 1033, a prime, which means Omega already knows you will one-box. If it were me, how I would switch from your optimal strategy to deterministically one-boxing before even knowing whether the number is a prime (I didn't know until I looked up; I'm speaking from the morgue right now) is beyond me.

I guess the lesson in this exercise is the same general argument Eliezer has made against lotteries: don't bet on outcomes you don't control.