With a post-'45 POD you could do one of the following:
1) Chiang initiates political reforms. They don't have to be successful, but it'll certainly boost popularity for KMT
2) Have the relevant authorities be smarter about reorganizing and downsizing the National Revolutionary Army. Use the experienced men to start a reservist system at their homes and give them better benefits - IOTL the demobilization forced a lot of men out of uniforms, and they all ended up joining the Communists for a living
3) Use New I and VI Corps, two of the best-performing and -equipped Chinese units in the war, as training cadres and start a Chinese version of Fort Irwin somewhere
4) BE MORE COMPETENT IN COUNTERINTELLIGENCE. I can't stress this enough - IOTL there were so many Communist spies inside the Chinese General Staff the Communists got the original copies of KMT battle plans. It was with those intelligence they managed to force the 74th (Reorganized) Division into unfavorable terrain at Menglianggu which resulted in its destruction, decisively defeat the ROC Army at the Huaihai Campaign, and elude Hu Zongnan's offensive against Yan'an.
5) Accept that Manchuria is a lost cause and do not bother to attack it, at least not until he consolidated the rest of the country - the Communists weren't the only ones causing trouble, remember...
6) If Chiang does end up attacking Manchuria, have him go the whole way and ignore Marshall's mediation. IOTL when the SecState tried to get the KMT and CCP to stop fighting, Lin Biao's forces were
this close to being forced out of country and into Russian Far East.
7) When the situation in Manchuria deteriorate to a certain point, start pulling out and fall back to the Yellow River's south bank. That'll give them more time to handle the East China and Central Plains Field Armies before any version of Huaihai happens
8) Somehow make Chiang Kai-shek less prone to interfering in battle
Stalin preferred a divided China to a unified China, and might urge the CCP to negotiate. I do not think that Mao would be given to do so. Whatever the case, the PLA is still going to have more problems than it did IOTL. You're not going to have a rapid nine-month advance from north to south, you're going to have a lot more destructive campaigns waged for central China since the Nationalists still have plenty of fight in them. It would be easy to extend the war a couple more years this way. This is assuming no major diplomatic action from the USA or USSR.
Pretty much this. At the very least, Fu Zuoyi isn't going to give up that easily at Peking, and without a Huaihai Campaign you could preserve the cream of the ROC Army.
Marc A