"Mega Evil" in setting.txt

[Q]

Yes you are right that if you put "false" the AI will not react at all if your empires gets really huge.
If you just want to increase the limit when the MEE takes place you should increase the "human empire percent" from 170 to some higher value e.g. 250. But still all AI will then very quickly break their treaties.
If you would like to increase the anger of the AI's slower you must go to individual AI anger files. You will find there a line about the MEE anger which is set to 50. As far as I understand, this means once the MEE level has been reached the anger will increase by 50 every turn, which is enormous. You could lower this to 10-20, but I never tried it myself so you have to experiment to find the appropriate value. If you give different values to different AI's you even should get different reaction times!
Hope this helps.