<div id="promptbox"></div>
<button id="update">Update Options</button>
<script>
var promptbox = $("#promptbox").kendoPromptBox({
    placeholder: "Original placeholder..."
}).data("kendoPromptBox");

$("#update").click(function() {
    promptbox.setOptions({
        placeholder: "Updated placeholder!",
        mode: "multi",
        rows: 3
    });
});
</script>