God Mode:
Use a text editor to edit the "defuser.ini" file in the "\ea games\harry potter and the prisoner of azkaban(tm)\system\" directory. Go to "Comma=" entry near the bottom of the file. Add the word "God" so that it now reads "Comma=God". Start the game and press [Comma] and you will never lose life. You have to press that key anytime you start a new challenge or activity.

Level Select:
Use a text editor to edit the "default" file in the "\ea games\harry potter and the prisoner of azkaban(tm)\system\" directory. Go to the "[HGame.HPPageFrontend]" heading and get to the "FirstLevel=HP3_Adv1Express.unr" entry. Change whatever value the .unr file has to any of the values in the "maps" directory.

Stronger Patronus Spell:
Use a text editor to edit the "spell" file in the "\ea games\harry potter and the prisoner of azkaban(tm)\system\" directory. Go to the "[HGame.PatronumSpell]" heading and change the "bAccumulates=false" line to "bAccumulates=true".