What do I need to do to swap out a VG248?
I conigures the IP address etc.., enabled the ports
Do I just configure the GW MAC address in CM and/or do I need to go into each DN and change the MAC as well?
Have a look at and make note of the specific settings on the VG (via console or telnet) before doing any changes. When you are ready you can go to the Device>Gateway Page on CCM and and change the MAC address from old to new and reset. You won't need to change the MAC for all the individual ports.
Hope this helps!