From the Dealer Site, go to the Customer then click on the customer name and then go to Customer Options on the left side. Set the Duplicate Codes option as shown in the screenshot below.

Now your customer will see a prompt to override the customer-wide duplicate rule, see screenshot below. This will not show if there is a duplicate on the same system as this is still not allowed. If they choose to override, then the audit trail will include a message that they added/edited the code and the duplicate security rule was overridden.
