We can switch AI types all we want with varying levels of aggressiveness (although making the necessary number of different types would quickly snowball into absurdity), but as Zardnaar alludes to, the only extent to which it works, it would be highly abuseable and doesn't really fit with the game. EaW's not like Stellaris or whatever where you can make a truce but you still need to worry about other factions because you can pass through borders, and then you'd also need some kind of underlying relationship modifier whichcouldn't really be based on anything, otherwise it's just request a truce, they have to stop attacking you, you build up and then you attack, after having shielded yourself from the one other person who may have been able to attack you at the time.