Main cable disconnect on meter unit

Hard to believe no one seems to be able to help you with this. There must be someone on here who has done this??
My best guess is that you'd need to gently pry the rubber boot away, to hopefully reveal how the plug is attached to the cluster's socket. Maybe/likely has some kind of latch/locking tab, or something like that.
If you have the new cluster, couldn't you tell how the plug attaches by looking at the socket? Maybe post a picture of the cluster's socket?

You were correct. The rubber boot doesn't appear to want to move, you have to really dig on it around the edges with a flat nose. Under is a connector that this fiddley but just needs a good yank.

Thanks for replying.

if you have the time, it would be nice to have a picture of the plug and the socket.

Welcome @juggermub! And thanks for posting the pictures!