It seems that Poland had a local version of Cuius regio, eius religio. The Warsaw Confederation signed the 28th of January 1573.
This principe applied to smaller territories than in the HRE, because in Poland, it was the szlachta family who decide to convert or not and the peasants need to follow the will of their masters.
I speaking about szlachta families who own importants properties, lands in scale of one or severals villages. Not the most humble ones, who were sometimes as poor as simple peasants. I imagined that the poorer part of szlachta will follow the conversion of the wealthier ones. Or not and it will a possibility of a religious war in the country as the rich and the townpeople will convert and not the poor szlachta and the peasants for example.
But you need to find an reason for all the magnates families and the middle class szlachta to convert to protestantism.
Financial argument seems not to be a possibility, because it seems, the Church were not very rich and there were little to confisct.
The best POD will be a polish born religious reformers similar to Martin Luther, John Calvin or Thomas Cranmer to become the leader of the Polish Reformation.