POD Bonnie Prince Charles succeeds in 1745 with French support.
the pricetag paid by Britain is that many global differences are settled amicably, including a very generous settlement of the Ohio valley being French. this butterflies the French and Indian War, and delays the European portion of the Seven Years War, as Frederick won't have an opportunity to exploit France/Britain being occupied elsewhere. Or, it completely changes up the European War (Britain won't back Prussia, for starters, as they don't care about protecting Hanover).
So, when the European conflagration hits, France still spends lots of money. when it's done, after not much gain, in late 1760's, King Louis is held in low esteem, and assassinated. This puts France in the control of a regency council, as the dauphin has died, and the new dauphin is underaged. yada, yada, yada, the revolution breaks out in the 70's.
meanwhile on the other side of the pond, the Stuart regime has adopted a policy of leniency to the various portions of the empire (Scotland, Ireland, the colonies), plus they haven't gotten involved in costly wars, so there's no need for heavy taxation. The empire muddles along, but sooner or later, the colonists are going to get too big for their britches and rebel, say in the early/mid 1790's.
ta da. mission accomplished.
and D'oh....I was thinking the American Revolution, not the English Civil War.
nevermind.