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] in 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.

Version 1.1
* Added an option to specify the date;
* Changed the default date to the current date.

Version 1.2
* Fixed a bug in the condition that was validating dates;
* Changed the TOC to require WoW 3.1.0 rather than 3.1.1 (Blizzard seems to have messed up with the interface version in the latest patch).

Version 1.3
* Just changed the TOC to require WoW 3.2.0 as the add-on is still compatible but was being shown as out of date.