I believe I've read on another forum (AHEMflightsimAHEM...) that Win 10 "protects" \Program Files and \Program Files(x86) no matter how you set you UAC settings.
As a great man said, which is better, un-installing/re-installing FSX and all the wonderful add-ons, or keeping struggling with this day after day?
As to cut-n-pasting the game it's self, no that doesn't work. HOWEVER, except paywares, most freeware, FSXBA F/A-18c, just for a wild, top of my head example
, can be simply cut-n-pasted to the new installation, no problem. I had a lot of problems with having to reinstall FS9 before I got FSX-SE, and I just got into the habit of zipping up the various folders that have add-ons. Things like \Guages, \Effects, and so on. Then I could just unzip them into the new installation, and tell it not to over-write. Poof! Add-ons installed. Only lengthy process was rebuilding the add-on scenery library. Small price to pay, IMO.
By the way, when I get the sim installed, and before I add anything at all, I always (now, anyway, could have saved a lot of head-aches if I had earlier...) zip up the game folder, everything. That way, I have a back-up of the "virgin" install, in case something (like me) messes up badly. I keep all my zipped up backups, add-ons and so on, on an external HD I can plug in easily, in case I want something off it. And with 7Zip, which is what I use, selecting individual files to unzip, and where to unzip them and so on, is very simple and easy. A huge plus for my poor ol' brain
Payware is a horse of a different color, but really, and I hope this is the case, as long as you keep the confirmation e-mails, with the registration codes, pass-words, or whatever, you are golden.
Hope all my rambling is of some small benefit...
Pat☺