Hello Dynamoxxx,
- Yes, many customer did the migration from IVR NON-NAT to IVR NAT without issue. There is disruption for IVR zone only, since the active zoneset need to be deactivated.
- Confirmed, IVR topology and zones stay intact after this process.
To migrate to IVR-NAT mode, follow these steps:
1. 
Stop or divert all applications on servers that depend on IVR.
–If CFS distribution is not enabled for IVR, then perform steps 2 through 4 on all switches where IVR is enabled.
–If CFS distribution is enabled for IVR, then enter the ivr commit command following step 2, step 3, and step 4 to distribute the changes to other switches.
2. Deactivate the IVR zone set by entering the no ivr zoneset activate command.
3. Enable IVR NAT by entering the ivr nat command.
4. Activate the IVR zone set by entering the ivr zoneset activate command.
5. Start or reestablish all application that were stopped in step 1.
The network can now run in IVR-NAT mode.
Also, you can use Fabric Manager GUI to enable IVR-NAT as follow:
1. SAN --- > Fabric xx --- > All VSANs --- > IVR --- > Deactivate Zoneset
2. SAN --- > Fabric xx --- > All VSANs --- > IVR --- > action --- > Check box "Enable IVR NAT" --- > Click enable button --- > Click CFS
3. Zone --- > right click IVR --- > edit Local Full Zone Database --- > Select zoneset --- > Activate
Hope this help
