You change your code. Loose coupling a nice goal to aim for, but at the end of the day, somewhere deep down inside the code, you have to tightly couple to actually get anything done. Where that transition occurs is entirely programmer's discretion.
It might be reasonable to make the assumption for some keys. In these cases a function taking the data and key as arguments and returning the value is sufficient and appropriate.
Frankly, if the code base is so littered with references to that specific data and key combination it might actually indicate a poor design.
Considering how easy it is, and how often I've had keys change on me, I have to strongly disagree.
"Frankly, if the code base is so littered with references to that specific data and key combination it might actually indicate a poor design."
That's kinda the point of the article.