Switch between Shipping Method

I have a case study where I want to implement a 10% discount on Prepaid Orders, similar to how we’ve implemented the Pre-Order Offer.

The issue is that we need to dynamically switch between shipping methods based on the payment option selected by the customer:

• If the customer selects Cash on Delivery (COD), the website should charge the full payment plus the shipping charges configured in Shopify.

• If the customer selects Prepaid, they should receive a 10% discount and free shipping.

Let me know how we can best implement this setup.