Locate the file defuser.ini in your installation folder and open it with Notepad. An example of this location for Steam users is "steamapps\common\bioshock\builds\release\". Locate the key you would like to bind the cheat to (F10 for example) and add the word "god" to the binding.
Save the file and start the game. While playing, press F10 (or whatever key you used) to toggle god mode on and off. The cheat may become deactivated when a video cutscene appears or you move to a new area. You may need to reactivate the cheat if you notice your health decreasing.
(supplied by: annerajb)
Using the same method as above, the following codes will also work:
|ghost||No Clipping Mode|
|teleport||Teleport to Crosshair|
|walk||Remove Fly and Ghost modes|
|killpawns||Kill All Enemies on Level|
(supplied by: AcidTBH, rich_is_bored)