CIMC will pick up a dhcp address, if dhcp isn't available someone will have to hook up a monitor/keyboard to give it an IP on boot. The SNS will come preinstalled with ISE but you will have to have console access to run through the initial setup. Either physically next to it with a monitor/keyboard, or once CIMC has an IP so you can access the java KVM.
It's not unusual to have the requirement of reusing IP's with an ACS migration. Assuming that the ACS authentication nodes are not being load balanced, there are two possible methods I would suggest investigating. Keep in mind that you can change an ISE node IP, but it can't be part of a deployment, it must be a standalone node.
Option 1: Setting up a temporary VM on a new IP
1. Set up a temporary VM in parallel as PAN/MNT/PSN, build out and test the new ISE "deployment".
2. When testing is complete, change freeze ACS and sync network devices with ISE.
2. Shut down one legacy ACS node and IP and register the first SNS appliance to the deployment as secondary admin node and MNT.
3. Shut down the second ACS node and register the second SNS appliance to the deployment.
4. Deregister temporary VM.
5. Promote second SNS to Admin/MNT.
In the temp VM scenario outline in option 1, you have 90 days of licensing upon install, if that's not enough you can issue the licenses/apply them, then re host them later on. ISE will complain about not having vm licensing, but that's only a nag right now, not enforced.
Option 2: Use one SNS appliances on a new IP and change it
1. Setup SNS on new IP, build out and test ISE.
2. Change freeze ACS and sync network devices.
3. Shutdown first ACS node.
4. Change IP on SNS appliance from ISE CLI.
5. Shut down second ACS node, and deploy/register SNS .
6. Deploy second SNS appliance with it's ACS IP and register it to ISE deployment.
