During Fall Gelb, Rommel and Guderian disobeyed direct OKW orders to wait for infantry before advancing. They only halted their successful advance at Hitler’s direct orders, which lead to Operation Dynamo.
So here’s the first challenge: have them disobey these orders and continue their advance so that the BEF and any forces waiting for evacuation in Dunkirchen completely destroyed.
This is rather easy, but here’s the next one: have this incident lead to Hitler being deposed by the military, forming perhaps a military junta to lead Germany through the war.
Plausible?