I'm fairly sure you can't do that without modeling; the fire most likely uses a texture that is used by many other models in-game and as such replacing it will affect almost every single fire effect in the game. Besides, the color of the flame comes from the particle emitter itself and not from the texture it uses. (the texture is actually white)
All of that is based on assumption as this is how most models work. I did not actually check the kobold model to get that information, if you really need me to do so, I will. I can assure you that wont change much, though.