You would not be overriding anything other than the stock spawn_loot.sqf found in the DayZ Code.pbo compiles folder. As Seven has mentioned elsewhere in this thread, you would be creating a new array of the same objects - in this case from the cfgLoot.hpp also found in the same .pbo file. - and switching the ones you modify with the default from that .hpp file with functions - in this case - from spawn_loot.sqf. You'd then override the default spawn_loot.sqf with the custom one you created by initiating it through the server mission init.sqf as Seven did with his custom loot tables.