To activate these codes, you need to find your save files in a folder something like
(.../My Documents/Amnesia/Main/) and then click on your profile name. Open the save 
file you wish to alter with notepad, and press [CTRL]+F. Then, search one of the 
things (Health, Oil, Sanity) and look for the command streams below. Once the command
stream is found, edit the number at the end 
(ex. edit [ var type="3" name="mfLampOil" val="0.000000" /] 
to        [ var type="3" name="mfLampOil" val="9999.000000" /] then just load up that
specific save file and the amount you entered should be granted to you.

Effect             Code
---------------------------------------------------------------
Unlimited Health - [ var type="3" name="mfHealth" val="9999.000000" /]
Unlimited Oil    - [ var type="3" name="mfLampOil" val="9999.000000" /]
Unlimited Sanity - [ var type="3" name="mfSanity" val="9999.000000" /]