Yes, that's commonly done. You should title it "Amended Financial Affidavit" or, assuming you are filing in Tampa, it has to be called "Wife's (or Husband's or Petitioner's or Respondent's) Financial Affidavit dated September ___, 2012."
The contents of this answer should be considered friendly advice, not legal advice (I'm a pretty friendly guy), and the answer should not be construed to constitute an attorney-client relationship. If you'd like actual legal advice, call me for a free consultation at 813-635-0222. Also, if you liked this answer as much as my big ego thinks you did, be sure to click the thumbs-up button!
Yes, in fact the rules say you have an obligation to update discovery such as the financial affidavit throughout the entire time the divorce is pending.
Sign up to receive a 10-part series of useful information and legal advice about the divorce process.