The body of this question asks specifically about the case where editing isn't possible. I'm going to give a broader response based on the question in the title.
We have a custom here of not editing people's p'sak-seeking questions for them, even when it's clear how to fix the question. I understand that we do this for educational reasons and to impress on them the importance of gathering information here but directing personal questions to their rabbis. I get that.
And yet, I feel it's unfriendly toward new users. While it's fair to expect more of experienced users, consider the challenge faced by a user new to Stack Exchange and Mi Yodeya:
- It's a Q&A site, not a discussion site.
- It's not an ask-the-rabbi service.
- There are detailed instructions about what types of questions are and are not welcome.
- They don't understand what it means to put a question on hold yet; even though both the boilerplate and individual comments explain it, anecdotal evidence suggests to me that many first-time askers see it as final, as shutting down the question.
- They might not yet appreciate the subtle nuances of wording; why is it bad to ask "can you X" but ok to ask "what is the halacha of doing X"? We're used to it, but I can see how it comes across as splitting hairs. Yes, we come from a fine, longstanding tradition of splitting hairs, but users have different backgrounds. Some of them have never been inside a yeshiva.
So in the case of a first or second question from a new user, where the intent is clear but the formulation of the question is problematic, I think it should be acceptable to fix it so long as we also leave a detailed comment explaining why we made the change and the importance of consulting your own rabbi for individual advice.
Instead of just giving them links to read, we can provide a positive example of how to fix a question that's otherwise going to get closed. This is welcoming in a way that "read this link" and a closure isn't, and it's still a teaching moment. If they don't learn from it then future questions will be closed, but we can help a new user have a better first experience. I think that makes it more likely that the person will have a second experience.
Nobody should feel obligated to do this, but it should be permitted. You'd help that stranger who wanders into shul and doesn't seem to know his way around the siddur, right? Well, we too are a community with not-always-obvious conventions, and IMO a demonstration of what to do will lead to a better experience all around.