People talk about plans for after the war - how do we know what plans may or may not be in place after the war? Did Britain have a plan for after the war when they went to war with Germany? Maybe they did I don’t know - or maybe they just felt the Nazi regime had to fall.
Not in the same sense, because the two situations aren't in any way similar and can't really be compared.
The US and Israel clearly want regime change in Iran, and while that was an obvious end goal of war against Nazi Germany, Britain did not initiate a conflict with Nazi Germany for the express purpose of toppling that regime. Indeed, in 1939 when war was declared, and certainly through 1942, there was no real certainty that Britain was going to prevail and have to consider what to do with post-war Germany in any case. WWII was a war of eradication, from the US and Israeli perspective at least, this action against Iran is not. The US clearly and understandably believes that if it had a mind to see it to conclusion it would ultimately prevail in a conflict with Iran, so it can think right now in terms of "what will we do after we win?". That's a wholly different proposition from the situation Britain faced in the first half of WWII or the Soviets were facing in 1941-43, because at those points in time they were fighting purely to survive and not really contemplating what to do post-victory.
From 1943 onwards that changed, and more and more thought was given to what on earth the victorious nations were going to do with the defeated ones, but even through the late 40s there wasn't always a consensus and it led to ongoing occupation, division, and the advent of things like the Berlin Wall and the Cold War.
Interestingly though, at the very first face-to-face meeting between Churchill, Roosevelt, and Josef Stalin, Stalin pitched up and immediately enquired as to what the others planned to do once they had destroyed the Nazi regime 😀