I thought I should share my experience about modding natives for the posterity. Norrefeldt if you include this info into your essential editing post above (#3) in your own style, I’ll delete this post to keep the thread clean.
Natives are coded by several numbers in the province.csv file. These are:
native combat strengh: This number determines the number of natives multipled by 100. Its value can go from 0 to 400 (40,000 natives).
ferocity: This number determines the tolerance of natives to colonials. A value of 9 will set spontaneous attacks every few years and induced attacks almost every time an army enters the province or a colonization attempt fails. A value of 0 will result in natives that almost never attack.
efficiency of natives in combat: This number determines how good the natives are in battle. In the game you can find preset values between 0.1 and 1.3. Very high values seem to be possible, but a big combat improvement over 1.3 has not been observed. A value of 1 or above makes the natives very tough against low land level player-controlled troops.
natives tolerance value: This is the number displayed in the tooltip box, and goes from 0 to 9. Albeit being labelled as agressivity, from no agressive to highly agressive, this number determines how much damage the natives do (colonists killed) when they succesfully attack the colony. A value of 9 means that one attack can wipe out a level 3 or level 4 colony. As widely known, this number also affects colonization chances. The AI will try to wipe out the natives when this number is 5 or higher.
From the above information, we can mod some curious combinations, like natives that attack often but do no damage to the colony, or natives that are strong enough to seriously damage colonies, and very intolerant, yet the AI does not kill them, effectively hampering AI colonization. It should be noted that the AI cheats on the efficiency in combat, and has as little problem to defeat natives as it has with rebels. This is probably a good thing, as the AI has no memory of how troublesome natives are, and after subduing them, usually moves the troops out, leaving no garrison to protect the colony.