Is there a way to run the rebasing tool in a "low risk" scenario, so that only stamped appointments are updated?

Q: Is there a way to run the rebasing tool in a "low risk" scenario, so that only stamped appointments are updated? ... skipping anything that is questionable like single instance?
A: you can do just recurring meeting.  is this what you are looking for?  please see http://support.microsoft.com/kb/930879/en-us  look at the section labeled "Options for udating Mailboxes"