Default behavior can be achieved in any number of ways.

A simple way is to hard code logic such that, “If File.Found, do logic from file, else do hard-coded logic here.”

This is not ideal, as you want your game data-driven and the code reusable, so the most common way is to check if an override file exists, do that logic if so, or do the logic in a non-deletable always-there default file.

Those are basically the main 2 ways.  From there, you can add as much icing on top by fancying up the system for replacing a default file.  Allow these 2 to explain:

Guy A: “I made my system so that if the file is in directory B, it uses that, otherwise it goes to the file in directory A.”
Gal B: “I don’t want people messing with my files so I encrypted the files in folder A.”
Guy A: “I don’t want people messing with them, so I encrypted them and hid them in a hard-to-find folder.”
Gal B: “I don’t even want people to notice that the system exists, so I have my default files hidden and encrypted, and when the override file is lost I copy my default file into its place.  This makes it look as if the file is always there, and my loading code only has to read the override folder, because it will always find either an override file or a default file that was copied into its place.”
Guy A: “I like your eyes.”
Gal B: “Here, you can have one.” *pop*


L. Spiro