On 11.4.x or newer, you can:
- Force all members of device group into offline mode except one.
- Create new self IP addresses on all devices.
- Modify the Device Properties (Under Devices Management) to change the sync, failover and mirror IP addresses to the new IP addresses. Do this for each device, on the device itself.
- Delete the old IP addresses.
- Config-sync the changes from active to device group.
If you're running 11.2.1 or earlier (and possibly 11.3.0 as well, I'm not sure where exactly it became easier), you will have to rebuild device trust in order to get the devices to detect the updated sync, failover and mirroring addresses.
Do this during a scheduled maintenance window to minimize impact of any unexpected outage (Even though this procedure I've suggested is relatively solid).