Adding fees to an existing loan

We are sending documents to be signed by a customer who is working out of state. Is it permissible to add the fedex fee to the customer's loan? These documents pertain to the customer's loan.

Would adding a mailing fee to the loan be new money; therefore, right of rescission would apply?

Allowable fees are a matter of contract and State law. Increasing the loan balance maybe a RofR trigger under certain circumstances.