Search notes:

Registry: HKEY_CURRENT_USER\Control Panel\Input Method

EnableHexNumpad

Setting this value to the (string) value of 1 allows to enter (hexadecimal) Unicode values with the Alt key followed by + on the num-block and then the number.
The following simple batch file (or command) can be executed in cmd.exe to set this registry value: 
@reg add "HKCU\Control Panel\Input Method" /v EnableHexNumpad /t REG_SZ /d 1 /f
Github repository about-Windows-Registry, path: /HKEY_CURRENT_USER/Control Panel/Input Method/EnableHexNumpad.bat
As per Wikipedia, users need to log off and sign in again to for this change to take effect.

See also

HKEY_CURRENT_USER\Control Panel

Index

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