Hi,
Auctiva doesn't condone changing the link because one of the key ways we earn revenue and stay free is through the customers that are directed to the Auctiva store from the store window. Each time a customer accesses and purchase your item through your Auctiva store, Auctiva gets a cut from eBay.
However, if there's a way to do it, and you can figure it out, more power to you.
-Mike