Service Call Contract Number update

When can one change a contract number on a service call?

Here's the situation. Serialized product is sold to Customer A with a service contract. Customer A transfers or re-sells product to their channel partner, Customer B. Customer B then sends product in for service.

The service people don't know what product shuffling has happened since the product left the factory, and they really shouldn't have to. They just create a service call, look up the product by serial number, and then fill in the problem info from Customer B over the phone.

When they are entering the service call they can change the customer number and contact but they can't update the contract number.

Even if they can jump to the Customer Equipment Card and change the customer and contact person there, or close the old contract and create a new one, they can't update the contract code on the service call.