Unable to register, Win10/different user context

Facing trouble when trying to register the add-on for my SSMS admin account when running SQL Assistant with that account in Windows 10 using SSMS 2014 (it works for the logged on account). I'm getting the old "Unable to register SQL Assistant Add-On because of insufficient privileges available to the current process. bla bla"

Run as admin is selected and I've even shut of the UAC completly - no change.

If I was to add this manually in the registry, where do I find the setting? Does the add-on also need some additional reg in the SAS file?

Hi. It generates a number of registry entries varying for different program versions, locations, etc.. I wouldn't do it by hand, not a simple task.

but first thing first, please verify that
in C:\Users\All Users\Microsoft\MSEnvShared\Addins you got SqlAssistSSMS.AddIn file. Open that file in notepad and check the path referenced within is correct.
then check %USERPROFILE%\AppData\Roaming\Microsoft\SQL Server Management Studio\12.0\Extensions\SoftTree Technologies\SqlAssist.vs\1.0\extension.vsixmanifest Also pen it in Notepad, check the path is correct
and lastly the same for
%USERPROFILE%\AppData\Local\Microsoft\SQL Server Management Studio\12.0\Extensions\SoftTree Technologies\SqlAssist.vs\1.0\extension.vsixmanifest

Hi. I noticed that there were alot of references in HKCU, so I won't do any registy editing yet..

1. C:\Users\All Users\Microsoft\MSEnvShared\Addins you got SqlAssistSSMS.AddIn file - Check!

For the following I've checked this for both my standard account and for my admin account:
2. %USERPROFILE%\AppData\Local\Microsoft\SQL Server Management Studio\12.0\Extensions\SoftTree Technologies\SqlAssist.vs\1.0\extension.vsixmanifest - Check!
3. %USERPROFILE%\AppData\Roaming\Microsoft\SQL Server Management Studio\12.0\Extensions\SoftTree Technologies\SqlAssist.vs\1.0\extension.vsixmanifest - the whole Extensions folder was missing. I've tried adding it manually by copying from local + reboot. Did not change anything though.

Almost forgot: the path in all files seems correct.

I suggest trying the following as the next step

Login to Windows using your SSMS admin account, I assume it's a different user account because you refer to separately to logged in user account. This is somewhat different as running a program using another user's account. The objective of that is to have the current "admin user" session cleanly map to the user's profile in HKCU.
Start SQL Assistant in Run as Administrator mode. Open Options dialog. Try re registering the add-on for MS Management Studio. I really hope this would do the trick for you.