Please look at this code. It adds a new button 'NextYear' to the datebox.
$(function(){
$('#db').datebox({
buttons: (function(){
var buttons = $.extend([], $.fn.datebox.defaults.buttons);
buttons.splice(1, 0, {
text: 'NextYear',
handler: function(target){
var opts = $(target).datebox('options');
var c = $(target).datebox('calendar');
var date = c.calendar('options').current;
date.setFullYear(date.getFullYear()+1);
$(target).datebox('setValue',opts.formatter(date));
$(target).datebox('hidePanel');
}
});
return buttons;
})()
})
})