The Bonus Package for X3: Albion Prelude has just been released on Steam. It's a free collection of script plugins that have been created by members of the Egosoft forum community. Egosoft has selected them as extensions that fit well into, and do not destroy, the balance of the game. To access the bonus content, simply install it from the store page. The Bonus Package will also show up in the DLC tab of the game properties, where you have the option to uninstall it.
If you have previously installed the non-Steam version of the Bonus Package, it is recommended that you uninstall it first.