The only thing that this add-on does is to add a /AFA console command to the game that you can use to parse your own achievement links and return completed versions of them with the specified date.
For example, to generate a completed [Heroic: The Fall of Naxxramas] on May's 25th of 2009 you would type:
/AFA [Heroic: The Fall of Naxxramas] 2009-05-25
Notice however that the bracketed text should be the link to the achievement from your achievements window, as it's not possible to make up achievement links.
Works with any existing achievement as far as I know.
