Options: Inf. Resources prevents the decreasing of all items (ammo,flare,dynamite,lumen,metal and so on) you can also use it to "duplicate" items, e.g drop them from the inventory and pick it up ( If you need specific items you can use the savegame method from Akira) Find Player Variables will populate some variable pointers, I would not recommend to freeze them coz if the engine does reallocate the objects you need to execute the script again.
You can "stack" the upgrade values (except item_detector_upgrade thats a bool ) that means higher value = higher upgrade level.
if you increase the max_stacks value then you need to consume any item to force the game to refresh the GUI ( Inf. Resources needs to be deactivated for this ) God Mode does what it says, full god mode for the player without any visual damage effects. Find Core(Reactor) Variables script will of course only work IF the current map does have a reactor ( you have to activate the script again if you load a savgame / another map )