How do you dynamically disable pickup/delivery in the checkout page?

Shopify Partner
22 3 5

I just had a merchant, in the states, asking about this feature and I was unaware this was possible. I thought the checkout was off limits for developers but she told me she currently had a shipping app that disabled the pickup option in the checkout upon certain state abbreviations. How would an app developer go about implementing such a feature, which APIs should I look into to learn more about this kind of functionality?