Change add to cart text based on category

What code would I use and where would I put it if I wanted to do the following:

Change the "Add to Cart" text to

"Add Sets of Product to Cart" based on what category a product is in?

I sell some of my products in sets of X units and other products in single units.

Thanks in advance!

Do you have a list of category ID values that add "sets"? Is this on the product's detailed information (e.g. product_info) page only?