With Developer Platform, is it possible to customize the store templates?

We need some custom behavior when the user presses the Add to Cart/Purchase button. I've registered for the developer platform and have checked out the templated site, but I don't see any references to the templates used for the commerce/store products. Is it possible to customize the templates for these?

Apparently this question was asked before: https://answers.squarespace.com/questions/23841/how-does-one-customize-product-templates-on-developer-platform.html

The one nuance is you'll need to commit your change to Git and push it to the server before being able to see your changes.