Man really stretching the memory here as I have not modified the game or played it in a long time...
I think it was tied to the fx 0 texture and used the same base as the phaser, so changing that point on the texture with paint or what ever you have to edit the bmp, or pcx file should do it.
Only problem I see with it is it will also change the phaser.
So what files are we talking about here do you have the texture you are planning to swap, you can add it as a attachment to help me think this through again. Mostly I played with starship textures they where easier to deal with.
Also with some textures there where two places you had to change them one was for single player the or was multiplayer.