We don't have an API for additional delivery fees.
For returns, we have a process where customer refund is calculated net of the return fee.
As you know, exchange means swapping an item with the exact same one because of an issue for which the seller is liable. As such, we don't have a separate API for the exchange delivery fee, either.
For a return caused by the customer's remorse, we advise the customer to enclose the return fee in the return package or transfer the money to a bank account.