As a preliminary comment, I'd like to point out that although you are asking about how restrictive the phrase is, its force in typical dialogue is the opposite: to give the choice to the other party. The restrictive version starts with you must.
In your example, the scope of discussion is limited to the file and the keyword. As written, there is more than the hint of a suggestion that the implementation is also limited in like manner, though an enterprising hacker may well find some other means of export.
On the other hand, consider the following example:
Question 768249: A man can travel 120 miles in either of two ways. He can travel at a constant rate of 40 miles per hour, or he can travel halfway at 50 miles per hour, then slow [down] to 30 miles per hour for the second 60 miles. Which way is faster, and by how much?
This example uses exactly the same formula: someone can do something "in either of two ways".
Answering Question 768249 requires one to consider just those two ways of traveling the 120 miles. That's the limit the phrase imposes on the scope of discussion.
However, it doesn't assert that those are the only two ways to travel 120 miles. There is an unlimited number of combinations of speeds and pauses the man can employ to travel that distance. The wording of Question 768249 doesn't invalidate those ways - it just asserts that it wants to limit the discussion to two particular ways.
In summary, the phrase "you can do it in either of two ways" limits the scope of discussion to those two ways, but it does not necessarily assert that there are no other ways. There may be other ways, or there may not. The phrase doesn't give you any information about it.