In Windows 10 1607 (Anniversary Update), Microsoft rolled out a new, stricter driver signing policy that requires drivers to be signed by Microsoft through the Dev Portal. Cross-signed drivers are no longer allowed. The restriction only applies to new installs of Windows 10 1607. Upgrades from Windows 10 1511 or earlier are not affected.
I would like to have my Windows 10 1607 upgrade install enforce this new restriction, just like a new install would. There must be some sort of registry or boot manager setting, or a certificate store that could be modified in some way to increase the restriction.