If by locked in you mean, only a subset of all possible world states are available, then yes, your first sentence is on target.
As to the second, it's not really a matter of the question making sense. It's a well-formed English sentence, its meaning is clear, it can be answered, and so on.
It is just that the question will reliably induce answers which are answers to something different from the scenario as posed, in which a) Omega is understood to be a perfect predictor, and b) all the relevant facts are only the ordinary state of the world plus a). In your scenario, the answer I want to give - in fact the answer I would give - is "I tell Omega to get lost." I would answer as if you'd asked "What do you want to answer", or "What outcome would you prefer, if you were free to disregard the logical constraints on the scenario."
Suppose I ask you to choose a letter string which conform to the pattern (B|Z)D?. The letter B is worth $1M and the letter D is worth $1K. You are to choose the best possible string. Clearly the possibilities are BD, ZD, B, Z. Now we prefix the strings with one letter, which gives the length of your choice: 2BD, 2ZD, 1B, 1Z.
The original Newcomb scenario boils down to this: conditional on the string not containing both 2 and B (and not containing both 1 and Z), which string choice has the highest expected value? You're disguising this question, which has an obvious and correct answer of "1B", as another ("What do you do").
It doesn't matter that 2BD has the highest expected value of all. It doesn't matter that there seems to be a "timing" consideration, in which Omega has "already" chosen the second letter in the string, and youre "choosing" the number "afterwards". The information that Omega is a perfect predictor is a logical constraint on the strings that you can pick from, i.e. on the "end states" that you can experience. Your "decision" has to be compatible with one of these end states.
It is just that the question will reliably induce answers which are answers to something different from the scenario as posed[...]
Why? I don't understand why the answers are disconnected from the scenario. Why isn't all of this included in the concept of a perfect predictor?
...[...], in which a) Omega is understood to be a perfect predictor, and b) all the relevant facts are only the ordinary state of the world plus a). In your scenario, the answer I want to give - in fact the answer I would give - is "I tell Omega to get lost." I would answer
Omega has appeared to us inside of puzzles, games, and questions. The basic concept behind Omega is that it is (a) a perfect predictor and (b) not malevolent. The practical implications behind these points are that (a) it doesn't make mistakes and (b) you can trust its motives in the sense that it really, honestly doesn't care about you. This bugger is True Neutral and is good at it. And it doesn't lie.
A quick peek at Omega's presence on LessWrong reveals Newcomb's problem and Counterfactual Mugging as the most prominent examples. For those that missed them, other articles include Bead Jars and The Lifespan Dilemma.
Counterfactual Mugging was the most annoying for me, however, because I thought the answer was completely obvious and apparently the answer isn't obvious. Instead of going around in circles with a complicated scenario I decided to find a simpler version that reveals what I consider to my the fundamental confusion about Omega.
Suppose that Omega, as defined above, appears before you and says that it predicted you will give it $5. What do you do? If Omega is a perfect predictor, and it predicted you will give it $5... will you give it $5 dollars?
The answer to this question is probably obvious but I am curious if we all end up with the same obvious answer.
The fundamental problem behind Omega is how to resolve a claim by a perfect predictor that includes a decision you and you alone are responsible for making. This invokes all sorts of assumptions about choice and free-will, but in terms of phrasing the question these assumptions do not matter. I care about how you will act. What action will you take? However you label the source of these actions is your prerogative. The question doesn't care how you got there; it cares about the answer.
My answer is that you will give Omega $5. If you don't, Omega wouldn't have made the prediction. If Omega made the prediction AND you don't give $5 than the definition of Omega is flawed and we have to redefine Omega.
A possible objection to the scenario is that the prediction itself is impossible to make. If Omega is a perfect predictor it follows that it would never make an impossible prediction and the prediction "you will give Omega $5" is impossible. This is invalid, however, as long as you can think of at least one scenario where you have a good reason to give Omega $5. Omega would show up in that scenario and ask for $5.
If this scenario includes a long argument about why you should give it $5, so be it. If it means Omega gives you $10 in return, so be it. But it doesn't matter for the sake of the question. It matters for the answer, but the question doesn't need to include these details because the underlying problem is still the same. Omega made a prediction and now you need to act. All of the excuses and whining and arguing will eventually end with you handing Omega $5. Omega's prediction will have included all of this bickering.
This question is essentially the same as saying, "If you have a good reason to give Omega $5 then you will give Omega $5." It should be a completely uninteresting, obvious question. It holds some implications on other scenarios involving Omega but those are for another time. Those implications should have no bearing on the answer to this question.