Hi Henry,
My suggestion for this would be to use just User Data. I have attached an scene file with such. This means, you have to drag the Node with the User Data into both, to send and to receive it. (Uncheck the Min max settings in the User Data!)
Or: set a data-port in the “receiving node”—which I have re-named in the example into “Real_set in XP02”. Here you need only to drag the “receiving node with the port in to the node with the dat to “feed” the node.
I hope this works for you. (With Xpresso, there is AFAIK no option to set global variables, perhaps Python or C.O.F.F.E.E. might help here if needed.)
To test this set up, please drag the Cube up and down.
All the best
Sassi