A payee has changed names. How do I relate the new and old names?

BinNYC

The old payee name was ABC. The new payee name is XYZ.
Can a synonym be created for ABC=XYZ?

NotACPA

There's no such thing as the synonym function that you reference.

Re: the rest of your question, How are you making these payments?  In Quicken Bill Pay, you'll need to create a new Payee and abandon the current one.

In Q itself, you can do a Find/Replace to make these changes.