How to create subdomains using htaccess?

First, you should set all subdomains to one directory in your web server config.

like this one below: 

ServerName  mydomain.com

ServerAlias   *.mydomain.com

Second, add this code to your .htacess file

RewriteEngine on
# SUB DOMAINS
RewriteCond %{http_host} !www\.([a-z0-9-]+)\.([a-z0-9-]{2,5})$ [NC]
RewriteCond %{http_host} ^(www.)?([a-z0-9-]+)\.([a-z0-9-]+)\.([a-z0-9-]{2,5})$ [NC]
RewriteRule (.*) /clients/%2/$1 [L]
# /SUB DOMAINS 

Finally, you should create a /clients/ folder in the main directory. Now every folder under /clients/ folder is a subdomain. 

For ex. If you have a test/ folder under the /clients/ folder, you can call the folder test.mydomain.com

How to change URL without refreshing?

You can change the URL without refreshing  with  location.hash  .

For ex: facebook and twitter use this method.

http://twitter.com/#!/username

Browsers use the # symbol as page anchors and you create your own prefix to catch the URL like #!
You can  listen to URL with  window.onhaschange  to send a XHTTP request when it changes.

Example:

<script type="text/javascript"> 

window.onhashchange = function() {

    var link = location.hash.replace('#!','');

// add  your XHTTP request code here

    alert('URL changed. Your link is "'+ link +'"');

}

</script>

<a href="#!/en/home/">change url</a>

If you wish to check browsers' onhaschange capability, you can use the code below:

<script type="text/javascript">
if ("onhashchange" in window) { alert('location hash is enable!'); } 

</script>