Without rewriting a lot of history and butterfly gore, potentially not. A rising power in the same sense as India or Brazil? Yes. But a great power in the same sense as China, or even Canada? Not really no.
Britain.
They can swear new oaths or being kicked out of the service, if they're lucky. If not they're tried and jailed, most likely to be pardoned within a few years. Most facing such prospects will rather go into exile.
No more or less so than they were of Isabella.
No.
Alright so we've established plenty of things that caused more problems than they solved, and how/why things couldn't go drastically different from IOTL (e.g. a WWII-esque UN/NATO treaty system), what could be changed for the better?
I'm sure this has been done to death before, but how could Dewey win the '48 election, and what would be the consequences? How does President Dewey handle the end of the Chinese Civil War and PRC control of the mainland? What about Korea? Or the Soviets becoming a nuclear power? What happens to...
Britain's Liberal Democrats, as pointed out by Meadow up thread, aren't a significant party in the sense that they're never going to take control. Canada's Liberals are much the same way. They're more a protest vote against the two major parties than they are a viable political platform...
Terminator seems quite late, Arnold was already a big star after the two Conan films. Changing his casting in Terminator just frees him up to do other roles; perhaps we see the third Conan movie produced.
But the Entente, with the sole exception of Wilson, wasn't interested in a lasting peace. Remember the US had a completely different experience in WWI than say France or Britain. For all the talk of the War to End All Wars, at least in my reading, none of the participants were interested in...