This generally looks good, although I do wish the system had taken into account the real reason for the colonial independence movements -- the Enlightenment.
Yes, taxes were the cause around which the British colonials rallied but the thing that really separated years of contented colonial empires and the age of revolution was the Enlightenment. As people came to question authority, and came to instead believe rationalism ought to govern in all things -- creating the scientific method, challenges to religious authority, the creation of social science, and ultimately revolutionary movements -- the idea of colonial empire became increasingly untenable.
The birth of the Enlightenment ought to trigger an increase in liberty, not tax rates. (And for that matter lead to many additional affects because it's really what led to the end of the renaissance and the birth of the modern age. It ought to be a huge in game event like the Reformation, and a big trigger for world shaping events all around the western world.)
I'd really hate to see colonies revolting in 1640 because of taxes. And I'd hate to see contented colonies in 1780 for any reason.