The Addon Manager will correctly list the scenery as "not installed", if you untick it. But if you re-activate, exit from the sim and start it again, it will surely listed as installed.
Of course, provided P3D will shut down cleanly. If, for any reason, P3D crashed on exit, it might have not updated the scenery.cfg, so is still "unticked", which means the "Active" flag of the area in the scenery.cfg is still set to "False"
Thus making it impossible to use your products or Flightbeams?
I don't really understand the question. Surely all our products and Flightbeam's are totally usable, if you use them normally, which means you only activate them when installing, and deactivate when uninstalling.
Maybe you wanted to say they are "impossible to use", if you have the habit of CONSTANTLY ticking on/off a scenery from the Scenery Library ?
If you think you are saving memory by doing this, then this has been discussed many times on the forum, and it might apply to other sceneries, but not ours or Flightbeam's, see the explanation here:
http://www.fsdreamteam.com/forum/index.php/topic,11037.msg85275.html#msg85275So, there are no reasons why you would ever want to constantly enable/disable the scenery, surely not for saving memory.