Communist edge in the Civil War in part came from the geographic proximity their guerilla bases had with the Japanese occupied territories during Japanese Invasion, which allowed them to take over Japanese stock weapons, recover occupied towns and villages, absorb surrendered collaborators, even some Japanese prisoners near the Resistance War's end. Their existence owed largely to their ability to survive Japanese counter-insurgency campaigns, but also to their ruthlessness in destroying and absorbing Nationalist guerillas in the same regions.
From such perspective, if you want the CCP to win the upcoming Civil War faster, you could
A) save a few communist units from their OTL annihilation by the IJA, the first and foremost of them was the Northeastern Anti-Japanese United Army.
and
B) give the CCP guerrilla more time and chances in their Post-WWII take-overs. For instance, there were even communist cells operating in Pudong, which was then just countryside but is today the most prosperous part of Shanghai. If by any chance, they could take Shanghai, it could offset the KMT-CCP balance by a great margin.
Neither A nor B was easy, and actually taking Shanghai was improbable, but they were not impossible. Given the level of American mistrust of Chiang, any delay such mistrust caused in airlifting Nationalist troops to the occupied territories might give the Communists more time in taking over these occupied towns, when the Japanese has lost their will to keep on occupying.
The impacts of an accelerated Civil War, won this way by the CCP, could be mixed.
A shortened Kuomintang reign could mean that no one paves the way for a Communist "Liberation". The Nationalist officials had less chance to indulge in themselves in a corrupt take-over they did OTL on assets in the occupied territories, and to created a spree of hyperinflation (which made the introduction of Renminbi looked like a salvation). This would reduce the populations' level of tolerance to communist methods and excesses. And as if Chiang did not establish in Shanghai a wartime industrial management system during the Civil War, Mao would have no such system at his own disposal when he nationalized those same industries.
More surviving faction within the communist party could also dilute Mao's own power within it. A surviving Manchurian faction of the CCP could mean that Mao never became the paramount leader he was IOTL, a surviving Shanghainese faction could potentially make the CCP closer to its urban and elitist self as it was in the 1920s.