After asking a question I continued to work on a solution. Later, I gathered more information. I feel that this additional information should be denoted so that it is not grouped with the original question. Is there a standard/preferred way to do this?
I see this a lot and I see it mishandled a lot.
First, if you have no answers yet you should just edit your question to include the new information. Don't add headings like "update" or "edit" or other meta information. Just include your code, clarify what you've tried, or expand on what hasn't worked. If there were comments asking for this, add a comment saying that you've updated the question. (Commenters are notified by the system when you add comments like that: they aren't notified about edits. On getting a notification they may return and write you an anwser.) After a day or so you should flag all such comments as obsolete and remove yours.
Second, if you have some answers, but you are not adding contradicting information, you should add the new information in much the same way, but you might choose to add it at very top or very bottom of the question, not in the middle of a sentence in the middle of a paragraph. For example if one of the answers starts "in version ABC of the product, you do it this way" but you're using version DEF and hadn't said so, you should add a whole sentence, in an easily-spotted place, that clarifies your version. You should also comment on the answer, something like "my apologies, I am using version DEF so this won't work for me. I've updated the question." The person may choose to remove their answer or to leave it for others with a similar problem.
Third, if someone gives you an answer, you try it, and it does not help, you should leave a comment on the answer saying so. You don't need to edit the question to add the information that "I tried closing and opening it again as suggested by [Whoever] but that did not help." As in the first point, leaving a comment will cause a notification. Editing the question or adding another answer will not.
Fourth, if you have answers and your update is invalidating them, you should probably ask a whole new question. For example you said in your question that you're sure the file exists, you're sure you have permissions on it, and you're sure it's in the right format, and therefore this error message is totally wrong. You've been given some answers based on that information, and now you realize in fact you don't have permissions. You've fixed up the permissions and are now getting a different error message. You should not edit this question to reflect this ongoing saga. Instead, if there was an answer saying "I think you're wrong and don't have permissions" you should accept it and add a comment saying "Yes, I was wrong." If there is no answer, answer your own question saying you were wrong about the permissions and accept it. (Don't delete the question. Leave it for others to benefit from. A lot of deleted questions can lose you your question-asking privileges.) Now ask a whole new question about the new error message.
Obviously the first is the easiest, and the nicest to answerers. That's why it's a good idea to stick around after asking your question, monitor activity, and edit as need be.
Edit the original post
How to separate edited information