Is it valid behavior to update question again if it has an answer?

Question

I've posted an answer for this Question. Initially the question owner accepted my answer. But later based on comment requests from Felix Eve the question owner updated his question (instead of asking a new question).

So Felix Eve gave answer and question owner accepted. Is it valid? You can find those details more clearly form their comments.

Here I'm not really worrying about my lost reputation (-15) ;)

Here my answer seems invalid. So do I need to delete my answer or can I suggest question owner about this?

Please suggest me.

Answer 1

There are updates and there are updates.

It is wrong to invalidate current answers

Questions like that are called chameleon questions and are not liked. See Exit strategies for "chameleon questions"

It is OK to provide context, details etc as long as already posted answers stay just as valid as they were

Providing code that did not work does not change essentially how code that works should look like, so this edit seems fair. If OP would edit to say "I tried code posted by Krishna Mohan but...", it would be bad. But he posted code he was using from the beginning, and that's not forbidden.

Last note

It is forbidden by help center to ask question about code, without posting that code. If you decide to answer anyway, without waiting for OP to post it, it is your problem. Same for broad question, if you answer one and it turns out OP didn't want that part of the broad topic he sketched. And so on. If you answer questions that have problems, don't be disappointed your answer does not shine when question is fixed.