// lets create some master spreads
var doc = app.documents.add();
var master_spread1_pg1 = doc.masterSpreads.item(0).pages.item(0); // edit the master spreads

master_spread1_pg1.marginPreferences.properties = {
	right: 12.7,
	top: 12.7,
	left: 12.7,
	bottom: 12.7,
	columnGutter: 5,
};

var master_spread1_pg2 = doc.masterSpreads.item(0).pages.item(1); //edit the other master spread

master_spread1_pg2.marginPreferences.properties = {
	right: 12.7,
	top: 12.7,
	left: 12.7,
	bottom: 12.7,
	columnGutter: 5,
};

master_spread1_pg1.marginPreferences.columnCount = 5;
master_spread1_pg2.marginPreferences.columnCount = 5;
var my_spread = doc.masterSpreads.item(0);
doc.pages.item(0).appliedMaster = my_spread;