In this case, I'm of the view that editing the title (and tags if needed) without changing the question is the best way to deal with this type of thing.
If we were to introduce a policy of editing question bodies, it not only risks invalidating answers, but adds significant confusion regarding context, and the reader's understanding. It also changes the raison d'etre of the question itself. If it's something that the asker thought was complex but was actually something you learn in your first week of Japanese, it's not up to the question to reflect this, but rather for the answers to point it out.
This follows the general rule that answers are for the answers section, and questions are unique to the asker. If we start mixing the two and making answers apparent in questions, it just doesn't work, and the whole trail of logic that you can normally follow from a question disappears (also making it harder for other people to answer if they have better answers to contribute).
Rather than this, I believe that editing the title is the best course of action. Firstly, this legitimately does help with classification, which is important, but it also doesn't change the actual question itself. Unless the question is in the title (which it shouldn't be -- it should be at least repeated in the question body), editing the title should have negligible impact to the question. If it would impact the question, then we can move the original title text into the question body, and leave it at that.
From another classification standpoint, editing tags makes sense, and also doesn't change questions at all. This plus editing titles, not questions, makes classification tidy without damaging the Q&A of the site.