Deleting a userpic and uploading a new one with the same keyword will change the userpic in old posts. Uploading a pic with the same keyword as an existing pic will change the keyword of the old one to something random (e.g., "pic#8387348"). Deleting a pic will change old posts that use that pic to your current default pic.
After testing
Date: 2008-10-03 03:43 pm (UTC)