An edge router termed a "service gateway" operates to reassign network addresses such as Internet Protocol (IP) addresses to a subscriber, such as when the subscriber is to be transitioned from a first virtual private network (VPN) to a second VPN. The service gateway obtains a new network address routable in a second VPN and applies dynamic edge network address translation (NAT) on an interim basis to provide instant access to the second VPN (following web-based identification for example), while a prior lease for an initial network address not routable in the second VPN is still in effect. When the subscriber attempts to renew the lease in due course, the renewal request is rejected, which forces the subscriber to re-initiate dynamic host control protocol (DHCP) procedures to obtain a new network address. At this point, the interim NAT mapping is removed and the new network address is assigned directly to the subscriber via DHCP. This approach combines the benefits of DHCP and NAT while minimizing dead time on the network and the processing overhead associated with alternative approaches.