I remember that question.
The worst part of that particular question that you referenced was that the person who asked it refused to describe why he wanted to do what he was doing.
That's a problem, because it indicates the user has probably fallen into the XY problem trap.
There may actually be reasons why this particular solution might seem to be right, ...
Adding my additional requirement (non-permanent solution) would sort of change the question itself.
Yes, yes it would. In fact, that would make your question a different question, which should be asked separately.
It is, however, a related question, so your new question should also link to the existing question, along with a clear statement that the ...
Would it be legitimate to post a "follow-up"?
Yes, if you have a problem that is similar to a crap Question, ask a new question.
If yes: How can i make sure to not get closed as duplicate?
Capitalize "I" and reference the previous Question (mention explicitly why your question is different too)