This achievement requires you to edit any of the game files. Right click on the game in your library, select properties and then the local files tab. Choose Browse Local Files and use notepad to open the player file in the scripts folder. Change any of the values, save the file and load the game. You may need to restart the game to unlock the achievement.
Afterwards either revert your changes or Verify Integrity of Game Cache (from the prior Local Files tab) so you can continue to unlock any remaining achievements.