As to how he would get on the throne this early, I was planning on engineering a succession crisis. Ernest Augustus' wife doesn't piss off Queen Charlotte, they have a son, George III dies, and George IV forces through a divorce from his estranged wife. Opponents seek out Ernest Augustus, as he is the oldest son who is married and has a legitimate heir. Feedback on the feasibility of this course of events is welcome. Dynastic soap opera isn't my favourite area of research. It would be okay to wait till 1837, but I was hoping for some earlier butterflies, since a lot of important legislation and treaties had already happened by then.
The reason I'm looking at this POD is because I wanted the conservative side of British politics to be stronger. I was concerned the High Tories would be opposed to an expanded empire and too many butterflies would be created, but I'm guessing from your responses that this opposition was over in the 18th century? That's fine because it means less headaches for me. I thought it had continued until the beginning of Victoria's reign.
As for the Boers, they probably did quite well OTL, seeing as they got what they wanted within South Africa anyway, but I was assuming a less aggressively expansionist British Empire might allow an independent Boer state, but since 19th century High Tories weren't opposed to expansion and British policy in the area was pretty much directed from the Cape Colony, I think it's a moot point.