Change gridmarket "buy now" button to "add to cart"

Hi,

I have the latest marketpress and framemarket/gridmarket installed. I have products in individual stores and not on the main store. I.e. xxx.com doesn't have any products but xxx.com/test1 and xxx.com/test2 do. On the main site, I can see a list of global products. Can I change the "buy now" button to "add to cart"? Can you direct me to the code where I need to make this change?