Modifiying/reverse engineering the exe is illegal.
You might say that no-CD crack can be used for the CD to last longer.But it is put to misuse.Those who don't own the game are using it.That's the whole issue of it.
Similarly I feel modifying the game content(kits,bats,etc) also illegal.
But the developers don't care as long as we don't sell it.Like if I make a kit & demand $1 for it,then EA would take it serioulsy I think.
I've heard that Counter-Strike first started as a user created mod for Half-Life.