And to back up Spyder's comment:
So create your brand new Broadsword graphic, name it my1337bs.jpg and put it in the data folder and see where it gets you.
Nowhere.
You must follow a certain naming convention, programmed into the game, in order to have these files work. It will look for those files to replace once the game boots up.
So in the end, you have to replace files in the game, files that are packed somewhere else, in order to get the desired effect. Thus, you are breaking TOS by modifying the game.