I am aware of the costs of editing old questions/answers as described in the question Trivial edits to old answers.
However, I'm not sure in what cases the specific edit of re-tagging an old question is worth the cost. Re-tags can an useful edit for old questions, as this would make them easier to find for people with the same problem. For the following, assume that the re-tag is both correct and substantial, such that it would be accepted without hesitation if the question was new.
So, in particular, should we re-tag an old question if:
- The question is of decent quality, but unanswered?
- The question is answered, but neither answer nor question have positive score?
- The question has a few close votes. (might be different depending on the votes being for a duplicate or other reasons)
- The question and all answer to it have negative score or are of low quality.
As for some background, the main reason I ask this because I have reviewed multiple re-tags of old questions lately, some good and some bad, made by the same user. While editing too much old posts is another issue, I have quite a lot of doubts when the edit, if good, is substantial enough.