Migrating SCCM CMG from Cloud Service Classic to VMSS on another Azure subscription

There is no direct migration path for this. You simply implement a new VMSS-based CMG that sits side by side with the old/existing CMG. Clients will learn about the new CMG as they connect to the site (on-prem or via the CMG) and will begin to randomly pick between the two. Once you are comfortable that all clients have connected and thus learned about the new CMG, you can decommission the old CMG. Clients will then only be able to use the CMG (if they attempt to connect to the old one, this will fail and they will then use the new one) and will learn that the old CMG no longer exists and will stop attempting to connect to it.

Sorry but he is wrong. You have to be a certain version per MS. 2107 I think is the last version that could have 2 CMG's on the same system. My SCCM Env is on 2303 and does not support duel CMG's. I spent and entire year planning around this assumption to only get on a call for 2 hours and then told I was not able to due to the version of SCCM I'm on. Also just so you know 2309 is that last version that will support classic. MS at this time has no solution other than deleting the Classic CMG and rebuilding and Virtual Set CMG. I have over 8 Terabytes of data on my CMG without any steps being supplied to move the data. Only option I can see it to redeploy all of my applications to the new CMG. Microsoft should check the facts before telling people the wrong information.

Thanks

Adam