game editors?

do you know those game editors that u can change a game w/. they have them for like command and conquer games where u can change the men and creat ur own men and stuff. i know they update or recreate the main INI files but can anyone explain it in a little bit more detail.how exactly do they do it? whats involved?is there any encryption to crack?
i know its a little bit confusing but i tried:D

Yea tiberian sun, i know they have editors out there but i think it would be cool to do my own. if u could post those files it would be great. thnx

Yeah if I remember correctly tiberian sun has got a couple of huge files in the main game directory that store all the info... cant remember the file type.... .mix files or something maybe ?

sun.mix , winter.mix .... etc.