'8' worked, but the result is not what I expected. It really add 10000 population but what for? if u don't have the build area which will spread out when the population reach 5000 and 10000 through normal means. This function works fine if you already are at the size of 10 for that city.
I have noticed this, the only ones I tend to use are the gold and mana options, the rest I just don't touch.
The population one, it increases the population just fine, but what it doesn't trigger is the expansion that comes with the increase population.
Maybe its one of those things that requires you need to get to 5000, then 10000 to trigger the expansion, but just jumping from 4750 to 15000 skips the expansion.
Hmm, I would experiment with it and have 2 options or something, where it increases the population to 4999, then 9999 and so on, but I am not a trainer creator, so I do not know how difficult it will be.