Changing your Customer Display Name Format in the QBO configuration page within the Recurly UI will not affect existing accounts already synced over to QBO. These existing accounts will still display the old Customer Display Name Format. Only new accounts will sync over using the new Display Name.
For example, if you originally used Email as the Display Name and now use First & Last Name, all accounts synced over prior to the change will continue to display Email. Accounts created after the change will display First & Last Name.