A service provider is migrating a customer's eBGP peering from legacy AS 65010 to a new AS 65020 after a network merger. The customer's CPE is still configured to peer with AS 65010 and cannot be reconfigured during the maintenance window. On the PE router (now in AS 65020), which BGP feature allows the PE to present itself to the customer as if it still belongs to AS 65010, so the existing eBGP session comes up without customer-side changes?