JQuery Ajax Request: Change User-Agent

It is simply impossible, you are not allowed to change the user-agent for XMLHttpRequests. I'm not sure if this is valid for Internet-Explorer, but the w3c specifies here:

The setRequestHeader() method

[...]

When the setRequestHeader(header, value) method is invoked, the user agent must run these steps: [...]

Terminate these steps if header is a case-insensitive match for one of the following headers:

[...]

• User-Agent

If you are using jQuery, set the request header in the ajaxSetup.

$.ajaxSetup({
  beforeSend: function(request) {
    request.setRequestHeader("User-Agent","InsertUserAgentStringHere");
  }
});