You might cross post this in the ArcGIS Desktop forum...
What I understand is this:
The default location for package download is:
"C:\Users\xxxx\Documents\ArcGIS\Packages"
This can be controlled on a machine by machine basis through the ArcGIS File Handler Utility. I don't know if it can be set globally for an organization, but I think not.
"C:\Program Files (x86)\Common Files\ArcGIS\bin\ArcGISFileHandler.exe"
Thanks,
Mike