I'm new here and also I'm new in using Magento. :) I found this question Replace "Add to Cart" button with an "Enquire" button linking to the "Contact Us" page is very similar to my problem - I need to replace "Add to cart", but only for some products (not all). I think create a new Attribute is the right way, but I also need to edit the frontend side (I'm not so good with php). Can someone help me? Thanks!
Your best bet is to find a Magento professional that can help you if you aren't proficient in PHP.
However, if you want to attack it and get your hands dirty and learn a bit, you'll need to do a little research on how to create a module in Magento and add a block.
In your themes catalog/product/view.phtml file is a call to the add to cart block:
A simple "if statement" around this block to where if your attribute is not set, output this otherwise output your own customer block should do what you want.