Hey great, another player for my Mod!!
Locate the userprofile.txt file and in it will be a line of text
Change that number to whatever you want. Note that the number will take into account the Human Player + all the AIs (8+1), so if you want 12 AI players, set the number to 13.
When setting up the parameters of your game in the main menu, DO NOT activate the number of civs button. You will note that the number of civs on the button will be the number you have already put into the userprofile.txt. file. Activating the button will cause the number to revert back to 8.
You will have diplomatic access to all civs in terms of negotiations, but once you set up an embassy, you will only have access to scientific info for 8 civs (on the science manager screen), which cannot be altered. And you do not have control as to which civs you will have that access with either. But you can use the diplomatic ability to give/request advances to monitor where you stand in relation to a particular civ.
You can also set the following number
If you set this number to a higher number than NumPlayers, then any AI cities that either revolt or are captured by Barbarians will create a new civ. You will get a global warning message every 10 turns though (small bug), but I have not noticed that this affects the actual pollution levels in the game.
Please let me know how your game is going too.