Vincent,
Earlier today I edited a couple of comments I made a while back, because the information I gave then was current truth then, but not accurate today. I made the edits so future readers of the post will not be led astray.
Edited additions or changes can and should be clearly identified by their authors in some manner. My edits today were inserted text looking something like this: (Updated dd/mm/yyyy: text text text.). Fortunately, WikiTree documents edits. G2G answers and comments are always “signed” to show the responder and, if the answer or comment has been changed, the editor.
I consider it inappropriate to change a question after it has been answered. If someone did that and it altered the context of your answer, maybe you can edit or hide your contribution.
Updated 06/09/2014 at 2:28 PM: Edited last paragraph to replace "you answer" to "your answer". I really did not intend to make my point so dramatically. Ouch!