It is very easy to change admin URL for magento
If you want to change URL from
http://www.example.com/index.php/admin or http://www.example.com/admin
TO
http://www.example.com/index.php/siteadmin or http://www.example.com/siteadmin
Here’s what I did (worked for me on 1.3.1):
1) Open <magento_install_dir>/app/etc/local.xml
2) Find this code:
<config>
.
.
.
<admin>
<routers>
<adminhtml>
<args>
<frontName><![CDATA[admin]]></frontName>
</args>
</adminhtml>
</routers>
</admin>
.
.
.
</config>
3) In that snippit of code, change
<frontName><![CDATA[admin]]></frontName>
to
<frontName><![CDATA[siteadmin]]></frontName>
4) Save the local.xml file
5) Remove everything under <magento_install_dir>/var/cache/
6) Remove everything under <magento_install_dir>/var/session/
Update:
7) Don’t forget to change permissions for the local.xml to read only. I would recommend chmod 440 or 444.
