I've asked this question before about a couple of months ago.I too needed some practice.My answers to this thread was that there was no way to change the pop in single player.But instead.....
1.click multiplayer
2.click okay for the first one selected
3.click create
4.make all the players to comp
5.go to settings and change the pop to whatever
there u go,the game is a little slower due to that it is multiplayer,this only works in rise of rome.------------------
Prepare for the Destruction...