The code below shows how to add the 'onBeforeSetValue' event to the numberbox.
(function($){
	var setValue = $.fn.numberbox.methods.setValue;
	$.extend($.fn.numberbox.methods, {
		setValue: function(jq, value){
			return jq.each(function(){
				var opts = $(this).numberbox('options');
				if (opts.onBeforeSetValue){
					var oldValue = $(this).numberbox('getValue');
					if (opts.onBeforeSetValue.call(this, value) == false){
						setValue($(this), oldValue);
						return;
					}
				}
				setValue($(this), value);
			})
		}
	})
})(jQuery);
$(function(){
	$('#n1').numberbox({
		onBeforeSetValue: function(value){
			console.log('onBeforeSetValue:'+value);
			return value>10;
		},
		onChange: function(value){
			console.log('onChange:'+value)
		}
	})
})