<script type="text/javascript" src="jquery.min.js"></script>
<script type="text/javascript" src="jquery-ui.min.js"></script>
link <a href="#" id="link" onClick="alert('Denied!')">download</a>
<script>
link_download='http://site.com/test.rar';
need_link_download='http://site.com/111.rar';
$(document).ready(function(){
$("#down").click(function(){
$("#hide").css("display","block");
$("#down2").attr("href",need_link_download);
})
$("#down2").click(function(){
$("#link").attr('onClick','');
$("#link").attr('href',link_download);
})
})
</script>

<div id="down">download before
<div id="hide" style="display: none"><a href="#" id="down2">click</a></div>