Let me copy the discussion in the comments of Dominic's linked question. The pre-history of this discussion was Dominic's question posted March 6 6:02, 2018 (all times are GMT+1), followed by Francesco's answer [b], and Dominic's edit [c].
[a]: Dominic's post (abridged): A topological space is homogeneous if (...). Does there a homogeneous Hausdorff topological space (...) for which every continuous self-map is either a self-homeomorphism or constant?
March 6 6:02
[b]: Answer posted by Francesco Polizzi (in its original form): Take the discrete space with two points.
It is clearly homogeneous and Hausdorff, and its only self-maps are the two constant maps, the identity and the involution exchanging the two points. - answered Mar 6 at 8:55 Francesco Polizzi.
[c]: Edit by Dominic of the question Mar 6 at 10:19, adding the assumption that the space is infinite and then after the comment [d] below: "EDIT. I forgot to add "infinite" in the original question." edited Mar 6 at 10:33
(the next steps are comments to the question)
[d] Well, you should not change the question once there is already an answer. In this way a perfectly correct answer becomes a wrong one. Please write an edit, explaining the modifications you made. – Francesco Polizzi Mar 6 at 10:25
[e] I disagree with you. Even if this corresponds to the original formulation, this does not deserve an answer, but rather an comment saying that the question should be reformulated. If this were the intended question, it would be closed as off-topic. – YCor Mar 6 at 13:06
[f] @YCor: of course you can disagree. At any rate, this was the question, it was unanswered, open for more than one hour and it also had un upvote. Sometimes it happens in life that people miss trivial counterexamples, this is not my fault. – Francesco Polizzi Mar 6 at 13:21
[g] That said, I still think that modifying a question with an answer, making a right answer a wrong one is a bad practice, regardless if someone finds such an answer interesting or not. – Francesco Polizzi Mar 6 at 13:22
Now let me comment further. I think (1) it's bad practice to modify a question after it's been replied, because it's a lack of respect towards the person who did the answer, who possibly did some efforts to handle the question. In a sense, it reflects that the OP does not consider the efforts made by the person who wrote the answer as worthwhile.
But it turns out that this judgement can be appropriate, when the answer consists of a trivial counterexample or just a link. (In my own experience, a case with possibly a little effort by the replier, and where the question was subsequently modified, is this answer.)
Next, I think and it's been discussed at many places, that (2) it's bad practice to post trivial answers to trivial questions (one reason among other being that it forbids the OP to delete the question; one other being to discourage homework questions - anyway it's not the point here). If a question has a trivial answer, it should be closed, and the trivial answer should be mentioned in the comments. If one can give to the OP the benefit of the doubt that there's a missing hypothesis, then it's better post a comment addressing this, rather than immediately voting to close.
If we had followed Francesco's request ([d] above) in the current case, what would have happened would be:
- a new post would have been done with the question excluding finite spaces
- As regards the original post, Francesco's answer would have been accepted, while the post would have been closed as off-topic.