This is a pretty simple AHC: Is there any way to make the Greek and Yugoslav invasions more successful for the Allies? Saving Crete isn't too difficult, considering that Student's plan barely came through when the 5th Mountain division was airlifted into the one airfield held by the Germans.
The real question is, how can the war on the mainland be better for the Greeks and Yugoslavs, especially for the Yugoslavs? I can think that a full mobilization would help, or for the government to accept the military's advice and try to hold the southern part of the country, but I'd like to hear your thoughts.
How, with a POD after 1935, can the Allies perform better in the Balkans?