The Bulgarian leader decided that he wanted to become Byzantine emperor. They converted from Christianity and changed from Khans to Csars, somewhere in the late 9th or 10th century. They changed in order to be on an equal playing field with the Byzantines, where as the Russians were claiming that they were the new Caesars of the Third Rome, the Second Rome having fallen in 1453. I think that outside of other massive changes to European history, the only way to get a Khanate of Russia is to have the Russians convert to Islam, then get involved in Golden Horde politics and have a Russian prince declare himself "Khan" and conquer the rest of Russia, ala Muscovy.