Dornil,
Once you have an effect mod that contains the particular file(s) related to that which you'd like to alter to suit your taste, you are equipped to do a surprising amount of your own modding using just a text editor like Notepad.
To make the cannon hit smoke darker, open such files in 3do/effects/fireworks as, e.g., 20mmSmokeBoiling.eff or 20mmSmokeBoilingBig.eff, or 37mmSmokeBoiling.eff, etc., etc., and alter the values in the lines for Color0 and Color1. These 4 numbers control, in order, the intensity of the red, green, blue and opacity applied to the texture invoked for the effect.
Suppose we have the following for a simple smoke texture where the .tga is a white smudge to represent a smoke cloud:
Color0 0.5 0.5 0.5 0.4
Color1 0.9 0.9 0.9 0.0
The first line sets texture color and opacity for the texture at its creation as a middle-value grey; the RGB numbers are all 0.5. If they were all 1.0, the smoke puff would be at the full white intensity of the texture. If all RGB values were 0.0, the texture would be made black.
The second line makes the texture a near-white by the time it disappears, by increasing the RGB values to 0.9. The opacity of 0.0 means the texture becomes completely transparent by the time the game timer ends its live time. If the Color1 opacity is larger than zero, the texture disappears suddenly at the end of its life because it still has some opacity and is visible.
Often times the RGB values are not all the same because the designer wants to impr a color cast or shit in addition to whatever the texture base color is. If one wants to make a smoke more bluish, the RGB values could be, e.g., 0.45 0.5 0.55. If reddish, then, e.g., 0.55 0.5 0.45.
9nce you start down this path, you'll be tempted to play with other values in the .eff files. This is how I first made my foray into modding. It can be addictive! For me it involves both my artistic and technical proclivities.