I know more about the Incas, and the fall of their empire, than I do about the Aztecs...
But anyways, Columbus arrives in 1492 to the Caribbean, but have exploration after that spread out much more slowly, so that small pox reaches and ravages the Aztec Empire before actual Spaniards arrive. Once they arrive, I imagine the Spaniards can still win, but with an even greater native population that in OTL..
Perhaps the Spanish keep the Empire as a vassal/tributary state/something similar, and, I don't know anything about the Aztec dynastical system, but have a Spanish controlled Kingdom...
then you can have a revolt about "taxation without representation..."