I think two key elements in 1944 would have to change, but not by much. The first would be Churchill’s ‘Naughty document’: his proposal to divide the Balkans up into British and Russian spheres of influence, with each empire’s percentage of the total influence in a particular country determined by agreement; in the document, Churchill proposed that the Soviet Union be allocated 75% and Britain 25% influence in Bulgaria. This is a bit of a peculiarity on Churchill’s part, because the adjoining countries, Rumania and Greece, were each divided 90:10 (Soviets controlling 90% influence in Rumania, the British 90% in Greece.) Yugoslavia was seen as concerning both empires, so was divided 50:50. Since Bulgaria was the buffer between future Soviet dominated Rumania and British dominated Greece, and was also adjacent to Turkey and the Bosporus (an area of sensitivity to both empires), logically influence in it should have been divided 50:50, making it another buffer state.
Historically, at the time that these secret negotiations were taking place in Moscow, 9 October 1944, the Soviets had been at war with Bulgaria for only a month, having declared war on Bulgaria only when their forces were already overrunning Rumania in an offensive that only began in the last week of August 1944. In September, Finland and the Soviet Union signed an armistice, which allowed the Soviet forces on the front north of Leningrad and on the Karelian Peninsular to be redeployed elsewhere.
Conceivably, the Soviet offensive might have been given a lower priority, with troops and supplies being prioritised to the Baltic States and East Prussia instead, delaying the commencement of an offensive that, other than denying the Ploiești oilfields to the Axis, served no strategic purpose in the drive into Germany. With a slower offensive in the Balkans, even of only four weeks, Stalin might have been willing to accept a Bulgaria that had ‘liberated’ itself and declared war on Germany prior to the arrival of any Red Army forces; presumably with a coalition government containing a large Communist contingent – local communists not beholden to Moscow and therefore more inclined to go the way of Yugoslavia.