alt Hacker NewsSleep key is scancode E05F
In registry "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Keyboard Layout"
Create Binary value named "Scancode Map"
Put in there: 00 00 00 00 00 00 00 00 02 00 00 00 3E 00 5F E0 00 00 00 00
That changes scancode E05F (Sleep key) into scancode 3E (F4 key).
Then logout or reboot for the change to apply. I actually looked up what would be necessary to do this change without a reboot, and it turns out that only WinLogon.exe is allowed to make the Scancode Map change.
A tool to help manage these kinds of rebindings is the Keyboard Manager in PowerToys.
As I recall it uses multiple approaches, so it isn't "just" a straight manager of scancode maps, but that also helps it avoid logout/reboot for the initial change to take place.