This would help quite a bit. Chamberlain historically comes across as gullible and all old-school thinking Germany will play ballChamberlain stood down because of the failure in Norway, so a better showing there would maybe have helped. But then he'd be the man who lost France, while Churchill with his navy connections gets seen as the man who enabled Dunkirk and defied Germany.
So it looks like we have to go back to Munich, and have him put up a stronger show against the OTL arrangement, although I'm unsure what could be changed. Perhaps when he arrives home, he does a more downbeat assessment - not so much Peace in Our Time, as Peace for Now in a troubled world. That could take away his reputation of being gullible or deluded (which is a bit unfair as he was buying time to prepare for the inevitable).
Other than that, you'd probably have to start rearmament a year or so earlier. Too soon and the UK ends up like Italy with obsolete technology, but 6 or 12 months earlier and it might be just enough to provide more equipment and better training, set up a few more shadow factories, have a few more anti sub vessels in train, and maybe get aircraft cannon ready in time for the Battle of Britain and have 6 pounders starting production in mid 1940.
He'd still be tainted by the loss in Norway or in France, but it could set up a storyline of Chamberlain as the man who planned and Churchill as the man who delivered.
Granted he has no 100% idea that Germany won't .. but he has enough intelligence to not look dumb.
Ego and belief that has got the little corporal to listen to reason is what gets him the wrap.