I think you mis-understand me.

If you rclick on most .exe files, you will see a choice on the menu that reads Run As Admin.
It doesn't give the user Admin rights to anything but that particular file, and only while it's running. As long as they don't have Admin rights to the folder, or anything else, they won't be able to get in very much mischief, if any.
What it does do is make sure the file runs with the max permissions, to ensure the .exe can do what it needs to do, with it's own accessed files, like an aircraft's files, scenery files, etc. Not the user, just the .exe file, see the difference?
I do not believe the user can do any more than granted in their Login status.

Give it a test: log in as a user, as if you were one of the visitors, after setting the FS9.EXE file to Run As Admin when it's opened by anyone, and see what you can get away with.

Of course, I may be totally out in left field, but I do know that the Run As Admin thing is pretty important to allow the sim to do any number of things it needs to. Not the USER, as I said, but the .exe file it's self.

Good luck. Glad you never updated to W10. It seems like every update they put out for it causes more difficulties for the sims, and simmers.
Then again, there are people that don't seem to have any trouble at all with it, so make your own decision. But read the forum threads to see other people's experiences when you get a chance