Amazon VPC announces a network interface setting to dynamically remove and add an auto assigned public IPv4 address on EC2 instances. With this capability, customers that no longer require an auto assigned public IPv4 address on their EC2 instance can remove the public IPv4 address, and if needed attach back a new public IPv4 address, by modifying the public IP setting on the network interface. Before today, once a public IPv4 address was auto assigned to EC2 instance it was not possible to remove it. It remained on the network interface for the lifetime of the EC2 instance.
Source:: Amazon AWS