The rules.ini (naming variations for expansions) is the core file of C&C modding. As indicated by the name, it contains the "rules" of the game – the properties of every object, weapon, warhead, etc. in the game. For any C&C game from Red Alert to Yuri's Revenge, this is the main modification file. For Generals and everything else based on the SAGE engine, the INI-system is more complex and wide-spread.
Disregarding the side functions of the other various INI files (like ai.ini or art.ini), there is no way to make any changes to the game other than what the rules.ini allows for1. Not everything in the game is customizable. Features that cannot be modified are called "hardcoded" features.
|Red Alert||redalert.mix → local.mix|
|Tiberian Sun||tibsun.mix → local.mix||The patches add a new rules.ini to patch.mix|
|Firestorm||expand01.mix||rules-equivalent is called firestrm.ini, the mix also contains a new rules.ini for regular TS.|
|Red Alert 2||ra2.mix → local.mix|
|Yuri's Revenge||expandmd01.mix||Called rulesmd.ini, for mission disk.|