The ASA can only use the IP address configured on its actual interface as the IP address for VPN. In other words this interface IP address is the only IP address the remote sites/users can use to form connection to the ASA with VPN.
I gather that the /24 subnet is just routed towards your current public IP address which is about to change.
I guess in this case you would have to start either using the new public IP address that is going to be changed to the "outside" interface or configure the /24 subnet and one of its IP address to your "outside" interface and use it for the VPN connections.
I am not sure how the interface configuration change is done through ASDM. I am sure it has its own section for it in the Configurations.
Naturally on the CLI you would go under the interface configuration mode and change it. Naturally this is a change that should be done during a maintanance break as it will cause a small outage in the connections. Naturally the changed IP address would have to be taken into consideration in the remote destinations VPN devices. I guess it might even be possible to configure the new IP address beforehand as a secondary peer IP address in the L2L VPN configurations of the remote VPN devices.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
[toc:faq]Introduction:This document describes details on how NAT-T
works.Background:ESP encrypts all critical information, encapsulating
the entire inner TCP/UDP datagram within an ESP header. ESP is an IP
protocol in the same sense that TCP and UDP are I...