You can provide your own formatting functions.
var testCustomTpl = new Ext.Template('<div>', 'User: {username} ', 'IsRevoked: {revoked:this.yesNoFormat}', '</div>', { yesNoFormat : function(value) { return value ? 'Yes' : 'No'; } }); testCustomTpl.append('userList', {username: 'aconran', revoked: 1});