The Changing Faces achievement is worth 10G and is unlocked by playing with a custom team.

From the main menu go to Customise Team and choose mens 100m. Then you will be given the option to choose a team member. Simply press right once, (or choose any character to your liking) accept your new team member. Then back up to the main menu making sure you save the changes. Go to Training mode, when selecting your country press [ Register or Signin to view external links. ] to change to custom team. Select the mens 100m and simply finish the race.