FWIW, I 'share' my addon scenery with my FSX, P3D V2.4 and FSX-SE installs.
In my case I created a separate partition (drive) and move ALL my addon scenery files/folders into that partition at the root.
Then I 'mounted' that 'addon scenery drive' into the EMPTY Addon Scenery folders in the 3 sims. I copied the Scenery.cfg
file from my FSX install into the other 2 sims in the proper location and I was up and running.
If one choose not to create a separate partition one could use a 'junction' to 'connect' the other sim(s) to the FSX Addon Scenery
folder. Just google 'junctions' for your OS.
A simple entry in a Command Prompt window will do the trick.
mklink /j d:\whatever c:\whatever
In my case I would use this:
mklink /j L:\SteamLibrary\steamapps\custom\FSX\Addon Scenery X:\FSX\Addon Scenery
In FSX-SE you delete the 'Addon Scenery' folder as mklink will create the folder'. The icon will look
like a 'shortcut'...a folder with a little arrow.
Here is a link to a page discussing the mklink process.
http://www.sevenforums.com/tutorials/278262-mklink-create-use-links-windows.html
Also, IF youtr Scenery.cfg file entries contain the FULL path address to each entry, just putting a copy of your
existing Scenery.cfg in the other sim should work OK.
Paul