Respectfully, I think this question has some issues with the understanding of the physical world; either that or I'm misunderstanding what you've written. To clarify, I'm going to assume that by macroscopic you're referring to the Newtonian scale (Atoms and bigger) and that by microscopic you're referring to the quantum scale (Protons, electrons and smaller).
This idea that what happens at the quantum scale is inherently random represents a misunderstanding of how we use mathematics to resolve from quantum to Newtonian scales. The Schrodinger's Cat thought experiment is supposed to teach us exactly that. OF COURSE the cat's life is not dependent on a single decaying particle; the whole point of the experiment is to show that such thinking is a nonsense. In reality, the random component is there to provide a statistical way of measuring what an individual particle's path may have been when measuring them by the billions.
A-Ha! (I hear you say...) But what about Heisenberg? His uncertainty principle PROVES that quantum movements are uncertain, meaning that magic and God and ghosts and clairvoyants are all real because the very intent of my observation changes the outcome, right?
Well, no. What Heisenberg's Uncertainty Principle is really trying to teach us is that the smaller things are, the harder they are to observe. To prove this, let's try a thought experiment of our own.
You're playing billiards in a brightly lit room. Where are the balls on the table? Well, you can see them pretty clearly. Why? Because photons are bouncing off them and into your eyes. Do those photons impact the trajectory of the balls? Well, actually yes. But, the impact is so infinitesimally small that we can safely discount it.
But then we turn off the light. No problems I hear you say; I have some very small ball bearings that we can flick along the table and listen for their contact with the billiard balls. Does this impact the trajectory of the billiard balls? Yes, but not too badly.
What about marbles? What about other billiard balls? Worse yet, what about bowling balls?
In quantum physics, instead of the particle we use to do the measuring increasing in size, the size of the particle we wish to observe is actually decreasing. That means that Heisenberg's principle can be summed up in two statements:
1) All observation is essentially the collision of particles
2) The closer in size the particle under observation and the particle used to conduct the observation are, the more of an impact the observation will have on the original outcome.
This means that intent to observe does not directly impact the outcome; it's the act of observation, for the reasons described above.
The purpose of this context is to get to a very simple point. When physicists say that the universe contains deterministic laws, they're serious. We can launch interplanetary probes, listen to news broadcast all over the world simultaneously and even cook our toast for breakfast all thanks to the reliability of those laws to operate in a consistent manner over time. The real question is whether that's all the universe can contain. Quantum physics does not prove that the universe also contains random laws, it proves that some of the deterministic laws we've discovered are not complete enough to explain things on a very small scale, largely because our attempt to make the observation gets in the way.
So; IF the universe can only operate in a deterministic way, then it would mean that free will has to be an illusion. I've written much on this topic on this forum so for brevity I'd suggest going back to previous answers for a more complete answer as to why.
But, your question is free will in our physical system. Assuming that free will is real, then what it means for our physical system is that our understanding of it is by definition incomplete because free will implies that you can choose to do something outside the algorithm. In other words, the universe has to be non-deterministic in nature, even if you can describe it as mostly deterministic.
In that sense, the answer to your final question is YES. the set of alternatives X can be stretched, because a set of alternatives implies determinism. Free will on the other hand is the ability to choose between those alternatives in front of you but also to create your own and choose one of them. You may (for instance) choose to walk away from the choice completely and start walking a new path. Was that originally in the set of X?
I don't know.
The truth is that the math seems pretty clear. So does our experience, and the observations we make on that experience. The trouble is, they're both telling us different things. It's up to the individual to decide which is true for them until we get better information.