This mod replaces The Grox as well as their buildings and their vehicles with my versions which you can find here.
You will need to reset your galaxy in order for it to take effect so backup your "pollination.package" and your "game0" folder (C:/User/[Username]/AppData/Roaming/Spore) and then delete the originals. When you next run Spore, it will generate new ones.
I also added a cheat mod that makes the Interstellar drive 1 to have the same reach as the Interstellar dive 5 so that you can go to grox territory to see if the grox were replaced (you can simply delete it once you've done with it).
It works on my game but please tell me if it does for you.