You can add a random civ in single player ( Except for yourself which I find very annoying too )
You can play as a random race if you do the right things. Someone posted information about this some time ago, maybe a year or more. I don't remember who it was or when it was. That person should get the credit. I just use it when I feel like playing a random race.
1. Go to your Documents\My Games\GalCiv3 directory.
2. Find the Prefs.ini file and open it in your favorite text editor.
3. Search for Player0Random=0.
4. Change it to Player0Random=1.
5. Save the Prefs.ini file.
6. Start GC3, then start a new game.
This is where things get different. The Choose Civilization screen will look odd. The left side where all your races are listed will be scrolled all the way to the end of the list, but none will be chosen. The right side will not show any information about the race you are playing since none has been chosen.
You cannot play this way. You need to do the following for every game you start:
7. Choose a race. It doesn't matter which one, so choose any you can see on the left side of the screen. If you don't choose a race, the game will not like it
8. The information about the race you chose will appear on the right side of the screen.
9. Click Next, and set up your galaxy.
10. When you get to Opponents, you will see that you are shown to be playing as the race you selected instead of a random race. Don't worry about it. You will be playing a random race.
11. Click on Start, and see what random race you are playing.
After you edit the Prefs.ini file, you will always play as a random race unless you edit the Prefs.ini file again. If you want to stop playing as a random race, edit the Prefs.ini file to change Player0Random=1 to Player0Random=0.