well, you could do it by copying and replacing the torpedo files, IIRC, the ones for the CG are CGphotorp.py and CGquantum.py in your scripts/tactical/projectiles folder, but that isn't really the best solution, since you are completely replacing the files. However, BCUT allows you to change the file which the Sovereign calls for when you fire the torpedoes. It is quite easy to use, and there is a tutorial. For more complex changes, you can also use Model Property Editor, which is a tool in the SDK that allows you to edit any attribute of a ship's hardpoint.