Posted as several people have enquired and I’ve seen several more seeking.
This is what worked for me, informed by a couple of sources on the net. I cannot be held responsible if it destabilises or kills your computer. Use at your own risk.
Presuming that you have cancelled your reservation for Windows 10 already.
Uninstall updates KB3035583, KB2990214, and KB2952664. The first two were mentioned by other users as connected with the Windows 10 upgrade. The third seems to appear around the time Windows 10 has downloaded and is ready to install.
** The important thing is to ensure these updates are not reinstalled or even left as options to install **
When you go to Windows Update and it prompts you to start installing your Windows 10 upgrade, start by viewing Installed Updates – there will be a LOT (over 300 on my machine). There is no sort or search, you’ll have to manually scroll through the list (expand the window to full screen and widen the install name until you can see the update number). Then select and uninstall the three updates mentioned above.
Ignore the reboot prompt until all three are uninstalled, then reboot.
When the system comes back up, go into Windows Update again, ignore the Windows 10 install, choose the ‘see other updates’ option, on the left just under the update text box.
You’ll see whatever updates are pending, plus the three you uninstalled, and Windows 10 will be under the optional tab but ticked for install.
Right click on each of these four items and choose ‘Hide Update’ from the menu.
Now install any other updates you have outstanding, reboot, and you should be done.
I’ve seen some notes on the net regarding the service process TrustedInstaller.exe running in background. This process can NOT be ended via Windows Task Manager. It also has files installed that cannot be deleted without permission from TrustedInstaller which is above any Administrator and System privileges. These files are in the hidden C:\$Windows.~BT folder.
Other notes seem to indicate that this process will, eventually, quit. I have not had issues with it myself.