If you can find where the logos are, you can just modify those files, and not have to re-export, but that only works if you are not leaving the other generals in game. Otherwise, you need to use the material editor to change the files that are referenced. Find the plane that has the logo on it (hopefully it is just a plane), and you can then hit M to bring up the material navigator, and change the file that is referenced in the third? tab. After that, it should all work out.
