Non-aggressive factions?

[Cannibalking]

Is it possible to make a faction non-aggressive?

Please use simplistic words, I'm not too text editing savvy!

[Agamemnon]

Let me further describe the question:
I CK or I were to add a faction, but make it almost senile, what would the process entail, or is there none?
Roma Surrectum managed to do it with their other rebel faction, so is this possible, and how?
And please use simple words, with no abbreviations.

[Cannibalking]

Let me further describe the question:
I CK or I were to add a faction, but make it almost senile, what would the process entail, or is there none?
Roma Surrectum managed to do it with their other rebel faction, so is this possible, and how?
And please use simple words, with no abbreviations.

YES, PLEASE.