Create Invoice with applied credit line and invoice line

We have a situation where our customers want to "swap" product they have already purchased for a product of a greater value.  In this situation, the customer has already purchased product where revenue is deferred over a specified time frame.  The invoice for the original product is already paid.  A few months later, the customer wants to return the product they have already purchased and buy new product for a slightly greater value.  We would like to create an applied credit memo line (as the original invoice had deferred revenue - we need an applied credit memo to credit the