I believe that that registry fix doesn't stop the reservation and downloading of the Windows 10 update, just its installation. So, I think, the fix doesn't stop KB3035583 from installing or maybe doesn't stop the gigabytes of downloading Windows 10 installation files, it just means that the OS won't be upgraded. Still, all that downloading and wasted space...
Best bet would be to set Windows Update in its settings to either check for updates but let you download and install them when you want to, or you can uncheck the box that treats recommended updates the same as important. That way those updates won't be installed on their own volition. Mind you, the second workaround will only work if MS keep on setting these Windows 10 updates as recommended instead of important. I presume that a security fix involving one of the Windows 10 type updates will push the update to important, so maybe the first workaround is safer. Just remember to visit Windows Update regularly to install security updates.
