Modding
A guide to editing the population numbers, from various forum members

Go to your ...\DynamicResources\Config folder, and open up population.ini.

Remove all the current settings and then paste:

FOR POPULATION LIMIT OF 200:

MaxPopulation=200
PopulationEntry=0,20
PopulationEntry=2,30
PopulationEntry=4,40
PopulationEntry=10,50
PopulationEntry=20,70
PopulationEntry=40,90
PopulationEntry=60,110
PopulationEntry=80,130
PopulationEntry=100,150
PopulationEntry=120,160
PopulationEntry=140,170
PopulationEntry=160,180
PopulationEntry=180,200
PopulationEntry=200,200

FOR POPULATION LIMIT OF 500:

MaxPopulation=500
PopulationEntry=0,50
PopulationEntry=5,75
PopulationEntry=10,100
PopulationEntry=25,125
PopulationEntry=50,175
PopulationEntry=100,225
PopulationEntry=150,275
PopulationEntry=200,325
PopulationEntry=250,375
PopulationEntry=300,400
PopulationEntry=350,425
PopulationEntry=400,450
PopulationEntry=450,500
PopulationEntry=500,500
---------------------------------------------------------

Further Instructions

1. First, in Windows 7 I had to cut and paste the Population.ini config file from its correct location in the game install directory to my desktop in order to edit and save changes to it. Windows 7 (and probably Vista) doesn't allow modification of files in the Program Files directory. Obviously once done cut and paste the file back to its original location.

2. You can change the values of the above numbers to make it so that one locker can support 500 population, if you wish. Or no (zero) lockers can support up to 500.

Changing PopulationEntry=0,50 to PopulationEntry=0,500 will make it so by default you can support 500 minions without a single storage locker. Unfortunately, you will need at least one storage locker for research later in the game so you should change every Y integer in PopulationEntry=X,Y to what you want your max population so you don't accidentally reduce the support by having existing or building new lockers.

Example:
PopulationEntry=2,20
PopulationEntry=5,25

becomes

PopulationEntry=2,500
PopulationEntry=5,500

Do that for each PopulationEntry line.

Keep in mind, 500 minions will mean a more taxing game for your computer. That probably will not be a problem if you are running a computer which is younger than this game is. You can always reduce the population if the game is running poorly although if your population is in excess of the cap that may cause problems. If in doubt, you can always start with 200 (or any lesser number than 500) and increase the cap from there as you find the need for more minions.

Thanks for reading and I hope this helps. I've tested it with my own game of Evil Genius game save which I began yesterday and then all too quickly hit the minion cap, everything is working. I've been using this mod since I knew where the physical disc was located; it's not going to break anything.