ESRI Addins are installed in a hidden folder AssemblyCache under Apptadata.
e.g. C:\Users\[YOU]\AppData\Local\ESRI\Desktop10.3\AssemblyCache\ {xxxxxxx-xxxxxx-xxxxxx-xxxxxx}
I prefer having addins as 'shared' on a network location and then setting the Regkey of the user machine to a network path where addins reside.
This is done here:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\ESRI\Desktop10.3\Settings\AddinFolders\ PATH STRING as KEY
This allows ALL users to be on the same addin, when upgrades occur it is simply replace the one addinx file on the network location... on a new instance (open arcmap or catalog) , the internal values are compared.. if different, the new addin is loaded locally.
If you delete an addinx ... on a new instance opening (arcmap), the addin is deleted from the local.
Doing the above does not require any 'silent uninstall'.
You can also go further and change
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\ESRI\Desktop10.3\Settings\BlockAddins to a value of =1 so that no addins can be added by the user... this keeps everyone using the same addins, toolbars and extensions.
There is other ways such as using the ESRIRegAddIn.exe ... but that is a different discussion.
