I read several solution about cloning a datepicker jquery, but in my case, the datepicker source element is already loaded by the DOM and instanciate by jQuery UI.

I finaly solve it using :

var newID = $th.attr('id').replace(/\d+$/, function(str) { return parseInt(str) + 1; });
		    $th.attr('id', newID);

		    // datepicker : remove icon (sibling/next)
		    // remove class : hasDatepicker
		    // add new datepicker
     			showOtherMonths: true,
     			selectOtherMonths: true,
     			showWeek: true,
     			showAnim: '',
     			showOn: "both",
     			buttonImage: "calendar.gif",
     			buttonImageOnly: true

Ressources :