Whew!

I got lucky!

At the time I made all the OS share the Message Store and OE settings, I had
created files withthe registry settings.
Applying tose files to each OS puts things almost back to square 1 (o, if
you are a programmer).

So next step, on the main OS, is to verify that all subscriptions are
included, etc.
Then create new .reg files and apply them to the other OS.

I got lucky!