1) Warmonger score is based on the economic value of the cities you captured (80% of it if it was a defensive war), and the number of war you declared.
Your warmonger score gives Combat Strength bonus to ennemy units while in their land (halved in neutral)
2) Long war gives war weariness. War weariness gives penalty to supply. Being over supply is really contraining.
3) Defensive pacts are far more present than in vanilla (and assuming you cared enough about having a big army and having friends, they are accessible to the player). Declaring war no longer break defensive pacts. Defensive pacts no longer chains each others.
4) War brokering is far more present than in vanilla (though difficult for the player to be part of, because the windows in which you can buy war from other civs is very short).
5) Peace brokering is only possible for the winner of a war (cf the warscore)
6) You can force your opponent to capitulate and become a vassal. (voluntary vassalage is also possible at peace time). Vassals always have the same War/Peace values than their master.
Is it what you asked for?
Those changed are partially documented on the wikia (
http://civ-5-cbp.wikia.com/wiki/Civ5_CBP_Wikia) and on the ingame civilopedia.
Any outdated/incomplete stuff in the ingame civilopedia is considered as a "bug", and report of those are welcome.
(The wikia is known to be outdated, but too few people have the will to update it)