Well, remember the KMT was quite left-wing officially; their platform called for socialism, they had sorts of left-leaning laws, like land reform, anti-corruption measures, etc. on the books. If Mao or someone more dedicated to those left-leaning ideals were in charge, those laws would probably be actually enforced. This would likely greatly undercut the Communist support base in the countryside, and lead to a Nationalist victory in the eventual civil war.
I see a Chiang-led Communist Party as being not really dedicated Communist at all, possibly something like the Viet Minh; more nationalist than Communist. They would stick closer to the Stalinist line in an effort to get more Soviet aid.
Of course, I have no idea how you go about switching them.