Thanks, Leo. You gave me the clue about what I was carelessly overlooking:
If it’s launched from the same window that is in Admin Mode, it will be launched as admin.
I had indeed been experimenting with the DOS box (amongst others) because that is very easy, as you say. But I had been elevating using a lister, then launching software through a floating toolbar --- the floating toolbar was, of course, not connected to the lister, so it didn't work.
I now find that when I launch using a button on the same lister, everything works as expected. Also, when you turn on 'Administrator mode' from a button palced on a floating toolbar, software launched by a subsequent instance of the same floating toolbar is not elevated (as one would expect).
So my original problem remains --- I was trying to use a global variable to insert the command modifier @Admin as a first line, or @Admin: in front of the command, an approach that worked perfectly with parameters such as NewTab in other DOpus commands (see my earlier post). Clearly modifiers work differently, which is what surprised me in the beginning.
As I said, no worries. I can script, or even easier, I can use a user-defined command with a conditional that insert @Admin explicitly if the global variable is non-empty.