I will consider the smaller scale scenario first:
---------As an alternative, consider a second, more modest version of the same scenario -
On his death in March 1953, Stalin's entire set of memories and knowledge from the last decade of life is inserted back into his younger self as of March 1943 - how does Stalin wage the 2nd half of the Great Patriotic War differently, and then the Cold War through the Korean War?
If Stalin from the late Korean War era has his mind and memories pop in to his mind and body ten years earlier, in March 1943, shortly after the Stalingrad victory, how can he increase Soviet success in WWII?
Can he direct the front in a manner, anticipating German moves, so that he can follow up the Stalingrad victory and not have Red Army's forces checked afterward at 2nd Kharkov by Manstein's "backhand slap"?
Could or would Stalin concentrate some air or ground force resources, right then in March, on recapturing the area of Katyn Forest area (Smolensk region), or bombing it from the air, to disrupt the German discovery or verification, photographing and broadcasting of the Katyn massacre evidence and delaying the emergence of western Allied suspicions, before the Germans did all this from April 1943?
Could personal knowledge he brings back (of Nazi moves, German vulnerabilities, organizational and technological solutions and mistakes) in time help improve Soviet operations to the degree that the Soviet front rolls forward against the Nazis months, or up to a year faster?
I would imagine, if possible, given how *this* Stalin remembers how the Cold War and Korean War later broke out, and the NATO alliance was started, he would want to at least try to finish the war in Europe with more of the continent under Soviet military occupation and legitimately diplomatically recognized as such.
Probably getting more of Germany and Austria would be first priority, but can be challenging, as the faster the Soviets advance and destroy Nazi forces, yes it does provide the opportunity for greater occupation--but Germany, trying to survive, would also rush reinforcements from west and south to the east to oppose the Russians, and that could make western Allied landings and progress swifter than our timeline as well. However, in addition to occupying more of Germany and Austria, perhaps all of it, Stalin would see occupying/liberating Denmark as a strategic gain since it is a strategic chokepoint on the Baltic.
If the Soviets were to succeed, through better campaigning informed by future knowledge, in occupying all of Germany up to its western borders, then it is possible for Soviet forces to participate in the liberation of the Low Countries and eastern France. There's no way for the Soviets to realistically cover all the ground of the Low Countries, and certainly not France, before Western Allied forces staging from Britain also land and local resistance rises up. The same also applies in Norway, where at most, the Soviets could advance further into northern Norway than historical, and that would likely remain a low priority compared to other parts of Europe.
The Soviet Union in an optimistic scenario (for Stalin) could have forces in place in parts of the Low Countries and Norway that could be used to leverage those countries into neutrality, but would not be able to shape them politically to support Communist takeovers. However, if sitting on the Rhine on the German side they could coordinate politically and materially with French Communists.
If the Soviet advance into Romania, the Hungarian plain, Yugoslavia and Austria at any greater speed than OTL, without a corresponding increase in speed of western advance up the Italian boot, the Soviets could well get some armed formations in Venezia Giulia and get more of say in the occupation of Italy.
Of course the mention of Yugoslavia brings up Tito and the question of what to do about it. For 1953-minded Stalin *what* to do about Tito is quite clear, kill and disempower the man, in whichever order. The only questions are about *how* and *when* to do it. Because the ideal situation for Stalin would be to still ultimately make use of the Partisan movement in Yugoslavia, and the Yugoslav Communist Party, or a Communist Party, just one that is completely broken to his will.
And in the Balkans in general, Stalin knows the outcome in Greece of Communist defeat. He more or less expected it. He watched and listened while Churchill proposed the "percentages" agreement and didn't disagree. (I am not aware of a quote where he explicitly agreed either). But given the effort the Greek Communists were able to put up for a few years, and the early Anglo-American controversies over it, might Stalin while sweeping the Balkans have wanted to sweep down into at least northern Greece, leaving Salonica, Thrace, Macedonia, their cities, and troves of captured Nazi weapons in the hands of ELAS KKE, (like in Chinese Manchuria), to tilt the balance of any Greek Civil War in favor of the Communists?
Or, knowing that pressing the Turks for territorial concessions postwar would fail, would Stalin made up an excuse to declare war on them and seize the straits, at least the Thracian side, while he had armies marching through Bulgaria *during* WWII.
Also, at the conclusion of WWII, knowing that his sponsored Azeri and Kurdish puppet states in northern Iran would easily fall after Soviet evacuation, and that Iran, despite the flexibility it was hinting at regarding a north Iran oil concession to the USSR in 1946, would ultimately reject it, decide to remain in perpetual occupation of northern Iran?
The end date of WWII in Europe, whether it fall on the historic May 1945 date, or months to a year earlier, is a significant variable for everything that follows, because it has direct bearing on how soon the Soviets can launch a full-strength participation in the war against Japan and absorb specialized American Lend-Lease aid in support of that task, about 3 months after VE Day basically.
But let's set that variable aside for the moment, hold it still and assume VE Day comes at the same historical time, May 1945.
Would Stalin want to do anything than historical with the Soviet entry into the Pacific War against Japan? OTL's results were not bad, relatively high gain in prestige and influence, for low losses.
But might Stalin want to ensure the Soviet declaration of war on Japan, and its assault gets started at least a week or two before he expects the first atomic bomb is dropped, instead of after? The reason would be to claim more prestige and credit and recognition for forcing the defeat of Japan. The Soviet effort would get more global publicity and notice if it hadn't started the day after the first atomic bomb. If the Soviets were really lucky, the Japanese would surrender after Soviet entry, but before the atomic bomb (there's a theory it was more important), giving the Soviets even *greater* credit and prestige for inflicting the final blow.
If Stalin were really greedy for credit, and perhaps a better chance to occupy all of Korea (after all, from his Korean War perspective, all of it is better than half), and perhaps some of the home islands, might Stalin initiate the switch to war on Japan after only a shorter gap after VE Day of just two weeks, one month or two months instead of three whole months like historical? What is lost from the build-up and preparations could be to great extent "regained" by the headstart in grabbing Japanese territory and destroying Japanese forces and defenses at the border, and more time to campaign in which Soviet forces of the first echelon, already superior in equipment and number to opposing Japanese, and surprising the hell out of them, reinforced by additional echelons being transferred from Europe over the weeks and months. The Soviets could potentially use an earlier start and more campaigning time (if Japan chooses to be stubborn and await getting nuked) to range their forces all through Manchuria and Korea, extend their operations into northern China south of the Great Wall, and move on from Sakhalin and the Kuriles to Hokkaido before Japan surrenders, creating a more advantageous political-military-diplomatic situation for the USSR postwar, and removing any need to fight a later Korean War. The extra campaigning time might be worth the risks of an earlier, less prepared, less spectacular, start to the fight with Japan.
Since in the Korean War, Stalin's cooperation with Kim Il-Sung and Mao was stable and effective, he probably would not have motivation to prevent their rise to power in this mind-time-travel exercise. And since the Americans were unexpectedly stubborn about defending their position in Korea and used Japan as a militarized platform, Stalin would probably be equally motivated as in OTL to participate in the Pacific War to match or increase the Soviet control over Korea compared OTL, and reduce the American monopoly on the occupation of the Japanese home islands if at all possible.
So those motives would argue for him to engage against Japan with haste equal to, or greater than, OTL.
-----After WWII, wherever the lines are when it ends, we then have Stalin with postwar decisions to make.
What would he decide similarly, or differently, from OTL?
As I was getting at before, I think he had come around by his death to viewing the Communist takeover of China as positive. So as much support and supportive behavior for the Chinese Communists as OTL, or more - not less. Same for Communist takeover in Korea in my view.
Stalin would know in advance a Berlin Blockade would not work, so he would not use that tactic, and might negotiate to avoid that type of interspersed occupation zone situation in general.
If Tito weren't dealt with before the defeat of Germany, he would be a priority after.
Stalin was already on the outs with Israel and had restarted anti-Zionist campaigns, and was upset by spontaneous Soviet Jewry support of Israel. On the other hand, he had no Arab friends or clients yet and was cynical about their governments. So Stalin, doing it all over again, might stick with a consistently anti-Zionist line, oppose the partition of Palestine in the UN, recognition of Israel, and direct that the Communist Parties of satellite states like Czechoslovakia prevent the sale and delivery of arms to Israel. He might seek to thwart post-war east bloc Jewish emigration of survivors to the west and Palestine (mainly from Poland, Hungary and Romania), but probably not as too many factions in those countries found it more convenient to encourage than oppose in postwar scarcity. On the other hand, Stalin may repeat what he did historically, and tactically support Israel, for the anti-British purposes he did in OTL.
