ArcGIS v10.2 and v10.2.2 store the addins in the common folder C:\Users\xxxx\Documents\ArcGIS\AddIns
where 'XXXX' is our account name.
So when you install an addin by double click, then the addin will be stored in this folder and spitted according the version.
You will have another 1 ,2 or 3 folders storing the addins..
example: C:\Users\xxx\Documents\ArcGIS\AddIns\Desktop10.2\{FD20EAB0-7ACB-4B35-AA41-753157745FD0}\waterutilitynetworktools.esriaddin.
So using the registry may be only a waste of time.