If it's really early in the vetting process (not a lot of activity/voting around your post), it may be acceptable to retract and "fix" your original answer. But long after the fact (after the original material has already been vetted and voted on), **I'd have to put that under "not okay."**

Edits are designed to improve, correct, or clarify specific issues with a post. But if you are fundamentally changing an answer long after it has already been vetted, you should probably preface your original post with a disclaimer and add another answer. 

I know that it's a bit "ugly", but remember that the core purpose of voting is to vet content. By changing the post substantially after-the-fact, you are essentially usurping all the votes used the vet your previous information and saying that your ***new*** information is now *de facto* "vetted" as correct also. 

Such activity would be inherently harmful. I'd add another answer to be vetted on its own merits and add a notice on your original answer to indicate how new information came to light. It's the only way to keep the integrity of the entire thread intact.