I need with a script for Joomla

I need help coding a script and integrating it in Joomla. Basically I need to change this:

<a href="http://www.xxxxxxx.net/click-xxxxxxx-xxxxxxx"

into this:

<a href="http://www.xxxxxxx.net/click-xxxxxxx-xxxxxxx?sid=username"

so I can track the username of a user that completed an action in my website by looking the statistics from my affiliate network.

 

I can do it just PM me.

 

Thanks for your reply, PM sent.