Hello,
1/ Simple products will be added to Cart, for variable products, where variations are not predefined, you will be redirected to single product page.
You can enable/disable this button via Theme Options > WooCommerce > Shop > Products style > Product Content Elements..
2/ Additional customization is not included in our support. If you need help with additional customization you can submit a customization request to the WPKraken team
Regards