From time to time there are questions that provoke answers that reach far beyond the initial question, for example, explain in detail some basic issues, or use detailed examples of some specific methods to answer a general question. Would editing questions' tags so that they apply also to such answers be ok? In most cases this would be adding broader tag to a question that is focused on some specific issues.
I believe this is a good thing to do. Tags are mostly a way to try to maintain the organization of the content on the site, and bear in mind that the real goal is to build up a permanent repository of high quality statistical (ML, etc.) information via questions and answers. Since much of that information is in the answers (more accurately, it is in the combination of the question and the answers), I think those facts imply that answers can be given some consideration in deciding the appropriate tags for a thread.