Turns out iTunes takes over the C:\Program Files\iTunes directory during an update in such a way that you have zero security access to it. Even if you are an Administrator of your own Windows 10 computer, you still cannot take over Permissions of the directory. It's completely and hopelessly hosed. Or so I thought...
Turns out Windows 10 comes with a "super user" Administrator account that is inactive by default that is perfect for situations just like this iTunes debacle (thanks Apple!).
To enable the Windows 10 administrator account do the following:
- Press Win+S and start typing Command Prompt
- Right-click the Command Prompt result and select "Run as administrator" from the context menu
- Run the command net user to display the list of user accounts on the Windows 10 system
- To activate the Administrator account, run the command net user Administrator /active:yes
- Click on the Start Menu
- Click on the Users icon (just above the Settings icon) and select the Administrator user
This will start a user session with the Administrator account which then you can do anything you need to in order to fix things like Apple's mess with iTunes automatic updates.
(As as FYI, I uninstalled every Apple product using the Administrator account, which actually required a reboot before I could uninstall iTunes)
Once you are finished doing your tasks as Administrator, go to the Users icon under the Start Menu and select Sign out so that you can log back in with your regular Windows 10 account.
Also, since there is no password on the built-in Administrator account, I highly recommend inactivating the account once you are finished with it. Just repeat the steps above and run the command net user Administrator /active:no instead to turn the account off.