If your existing answer had received votes (up- or down-), I would restrict edits to improvements on that answer. If it had not yet received any votes, I say go ahead and change it completely if you want to. I believe that edits within the first few minutes of posting are absorbed into the "initial" version of the posting. After that, there's an edit history.
I don't have a strong opinion on multiple, separate, answers by the same person -- versus one consolidated answer with many variations. I've seen both here. The all-in-one model can showcase your encyclopedic knowledge as well as point out pros & cons between them. Often, a multi-answer post will be community wiki so that others can add their ideas. The separate-ideas as separate-posts model lets the community vote on ideas that they prefer (for or against).