Sorry, I’ve had enough re-installations for this week, maybe month.
I think this GAC installation/un-installation should be done from the extension since it’s for its own use. So error-handling imho is to be done there.
Also, uninstalling the “program” should remove the extension automatically the same way it adds it automatically (without prompt to the user) in the installation phase.
Last point is linked to this topic - I think the components in the Visual Studio Toolbox should be added/removed by the extension installation/un-installation and not via registry.