To get less damage, edit the "defuser.ini" file in the "\ea games\harry potter and the chamber of secrets\system" folder. Scroll down to the end of the file to find the following lines:
[HGame.Harry]
bInvertBroomPitch=False
bAutoCenterCamera=True
bMoveWhileCasting=True
bAutoQuaff=True
fDamageMultiplier_Easy=1.2
fDamageMultiplier_Medium=2.0
fDamageMultiplier_Hard=3.0
Change the values of "fDamageMultiplier_Easy", "fDamageMultiplier_Medium" or "fDamageMultiplier_Hard" to 0.1.