2. Counterfactually (Retrodictively*)
In more detail…
1. Cf. Aristotle and Diodorus on the master argument.
What happens tomorrow makes true or false what you say today.
2. Cf. Nick Huggett's Everywhere and Everywhen, Hempel's theories, Musser's Scientific American article on free will, etc.
I think Musser's invocation of the block universe to explain retroaction is probably fallacious. I'd have to re-read the article, but the problem basically is this: the whole point of the (Minkowskian) block universe is that time is static, and therefore it's illicit to say action a at time t', after time ti, alters the conditions for action C(A) at time t. In a block universe, nothing changes.
Even so, it is not all that startling a claim that we can alter prior conditions. It is a possible property of our universe at time t-alpha (the putative origin of spacetime as we know it) that from the initial conditions Ci, there will occur X number of sandwich-eatings. It is also a possible property of the universe at time t-alpha that it will contain X' number of sandwich-eating events. If tomorrow I eat a sandwich, and then at some time t-omega the universe ends and the sandwich-eatings are tallied, I'll have brought the number to X. If, however, I don't eat a sandwich, the number will end up as X'. So whatever I do , I will decide a property of the universe at time-alpha, even though I am vastly far removed from it in spacetime.
His point about the impossibility of copying oneself, due to quantum indeterminacy, was, however, extremely apt. Down with Moravec! Down with Kurzweil! The singularity will not be televised!
Further, in any case, there is this worry: if a natural law's "authority" is based on its holding good at all times (i.e. ∃x∀t(Lx(t))), then a law can only said to be lawful if it holds at all times including all future times. Therefore, a law's putative lawfulness depends now on its holding-good at any and all future times. So a law's present status depends on future conditions.
In addition, Huggett discusses how a (hypothetical) future state of affairs (SoA), accessible by a time machine, would render certain SoA in the present impossible. E.g., my going into the time portal now at time t would be rendered impossible by my future self's persuading my past self not to enter the time portal at time t–x. Likewise, my entering the time portal in a red T-shirt at t would be rendered impossible by my future self deciding and succeeding to prevent my past-self-in-a-red-T-shirt from entering the time portal at t–1.
3. Some of what makes STR true is the general theory of relativity (GTR), but what makes GTR true is the total state of the cosmos at any formulation or enunciation of GTR. Thus, the truth of GTR depends on factors in the universe to which STR says no one can have access. In other words, we know GTR is true because it extends to the STR-relative states of the universe anywhere, but knowing GTR is true in that way transcends the limits STR says we cannot transcend. To be more precise, GTR's truth-being-made depends on factors operant in the cosmos even at times beyond which we could possibly observe. On earth we never see the sun immediately (without telescopes, etc.), but are always seeing it as it was about eight minutes earlier. This means the sun's current SoA is in the future relative to us. The same holds for cosmic factors even farther removed than the sun. GTR is true in the present based on the operant actuality of future phenomena.
4. What I do now can easily be modulated or negated by its impact on the future. Being green, for example, has (perhaps) everything to do with being ethically responsible towards our progeny (i.e. towards the future as an ethical condition on the present).