Can you change things to get Germany in the war past 1946? Sure.
An early change that would have ripple effects on the whole conflict is Hitler waits until September 1940 to attack France. Assuming the French military reacts as stupidly as they did regarding the attack France again falls. This time a large segment of the BEF is captured.
What happened in the months before then is FDR in the summer seeing a stalemate in the West decides not to run again and by the time France falls its too late to get back in as the dems have their candidate. Wendell Willkie wins in a squeaker promising to keep America out of another European war.
The British are left with a weaker hand and are seen to be weaker by the rest of Europe. Yugoslavia doesn't flip and sides with the Axis and helps Italy take Greece. Italy in Africa does somewhat better against a smaller British force so that Germany doesn't have to send troops to help them until the spring of 1942.
The invasion of the Soviet Union is only delayed somewhat. It happens June 1st 1941. Germany has more tanks, more men, more trucks, etc on hand for the attack. They also have troops from Yugoslavia with them. Leningrad falls, Typhoon is successful enough to screw up Moscow as a logistical hub.
Nothing like Lend Lease happens. Willkie avoids putting an embargo on Japan until mid 1942. Japan doesn't attack the U.S. for another year and when it does Germany doesn't declare war on the U.S. as no Lend Lease and no undeclared naval war.
In this timeline if Germany doesn't accept peace offers from the Soviet Union in 1942 or 1943 the war in the East rages on for years. The two countries end up coming to the table after they bleed each other dry. The British end up being pretty ineffective in this timeline thanks to the loss of most of the BEF and no Lend Lease. Churchill is ousted after the defeats in the East and in late 42 in Africa. By 1943 the broke British government makes peace with Germany.
Now if you want a timeline closer to ours where Germany survives until 1947 that would be hard. Kill off Hitler and fat man on November 1st 1941. Himmler tries to take power and within three weeks he is killed off along with the top level of the SS leadership. A military junta takes power and the SS in the Soviet Union is folded into the army. No DoW against the U.S. happens and FDR can't get the U.S. into the war in Europe until 1943 after a series of victories in the Pacific with an American public ready for war in Europe. The Manhattan project goes slower then OTL because of Hitler's death, no Final Solution, and the U.S. not entering the war in Europe until later. There simply isn't the same rush among the scientists to build a nuke.
In this case lots of interesting changes could happen. The Soviet's and Germany reaching a peace in 1943. Germany focusing its attention on fighting the British and the Americans. Stalin after three years of preperation re-enters the war in 1946
The Americans invade mainland Japan in May of 1945 and suffer massive losses, but achieves victory. The American government and public fears that an invasion of France will suffer the same kind of losses. In this situation Anglo-American hated of Germany is there, just not near the level OTL after Hitler and Himmler's deaths. The first two nukes is therefore is used in a battlefield setting to wipe out German forces defending France allowing for an easly D-Day in May 1946. By the start of 1947 Soviet and WAllied forces are knocking at Germany's gates two years later then OTL.
See, now both of these timelines sound really interesting I like the first because America under Wilkie staying out of the war is very internally consistent with the pro fascist and pro Nazi leanins of many AMericans in the 30's and very Early 40's.
Their were a lot of important Americans who thought Adolph was a really neat guy, and agreed with many of his policies, so I can see another "Too proud to fight" dictum under Wilkie.
That is going to bite an unprepared America in the butt in a generation.