Sure you can edit your question/code if there are no answers. Just don't place alternative code-junks without adding the comperative-review tag.

Replacing the code in question is fine without tagging it.

If one is doing a review at the same moment he/she will maybe place a comment asking when you will be finished (I did so on another question). If you see such a comment you should place a comment as well answering the question. Otherwise the reviewer may be loosing interest in your question.

After you get an answer you won't be allowed to edit your code. Adding some methods/classes which are requested usually don't hurt.

Sure you can edit your question/code if there are no answers. Just don't place alternative code-junks without adding the comperative-review tag.

Replacing the code in question is fine without tagging it.

If one is doing a review at the same moment he/she will maybe place a comment asking when you will be finished (I did so on another question). If you see such a comment you should place a comment as well answering the question. Otherwise the reviewer may lose interest in your question.

After you get an answer you won't be allowed to edit your code. Adding some methods/classes which are requested usually don't hurt.