So a bit of history. In the beginning, games were so simple, they didn't have any assets (think pong). Then as time passed, games started using 2D sprites for their graphics, but everything was always static and hard-coded.
The modern way is "dynamic loading", where instead of adding tanks into the game, you add vehicles, and have a vehicle type of tank. This is the system Chaotic Rage uses, so there is a configuration file in the data directory which has the information about what makes a tank a tank (weight, speed, accelleratrion, 3d model to use, sounds to play, etc).
All of this information (players, ais, gametypes, vehicles, objects, etc) is organised into a "Mod".
Chaotic Rage now supports multiple loaded mods. The system was in place for ages, but nwo the GUI works.
You have normally one or two mods, the "base" mod (chaotic rage), and optionally a supplementry mod, which is user selectable. Theoretically you could have additional mods loaded, but you need maps which can make use of the extra objects that the mods provide.
I've also added support for mods to contain maps (seperate from the stock maps which come with the game), so if you create custom objects or gametypes, you can create maps to go with them.