Add variables to all permalinks in site

I need to add variables to all links in my site based on a condition.

So all permalink in a page that met my condition (in specific category or whatever) : http://ift.tt/1K3KRES or http://ift.tt/1zAqsyX would be http://ift.tt/1K3KREU and http://ift.tt/1zAqpTC

How can i do that?