After you reach the desktop for the very first time, run a command prompt as an administrator to run this command: bcdedit /set {default} bootmenupolicy legacy
Restart and then press F8. The classic F8 options will show. Select Disable Driver Signature Enforcement. You must do this every boot unless the modded ACPI.sys can be signed. And, this way is easier than having to hold shift as you press the restart button.