I'm developing a Shopify app for my store using CarrierService API. This API gives me the ability to provide a custom shipping rate for a specific product and show them on checkout. I also have other legacy carrier services setup on my store like FedEx, USPS etc and they are also showing up on checkout as usual. At this point, I also want to provide my calculated rate for those legacy carrier services. But I don't find any way to provide a custom rate for any legacy service through the CarrierService API.
My questions are: -
Is it possible to manipulate those legacy carrier services on checkout?
Can I get and set the shipping rates for legacy carrier services?
Can I hide the legacy carrier services from the checkout in some cases?