PC Remote - Screen Brightness and Power management

Hello folks.

For a <> onboard computer (Dakar type truck), I use a matrix keyboard glued on the dashboard to control GPS, sound, data monitoring (via Processing), emergency broadcast (GSM shield). This keyboard controls the PC via an Arduino Micro.
This excellent tutorial provides me control of the sound.

I’d like to emulate other functions such as screen brightness or sleep mode.
ASCII codes won’t send this orders through the HID emulated keyboard.
Is there any modification on HID or USBapi files to add more <> keys?
Thanks a lot.

PS: The computer is an Acer 3680 fanless with SSD, turn into tablet with a thick plexiglass screen (touchscreen would break within hours under the Sahara heat + vibrations).

This might be a starting point - http://stackoverflow.com/questions/27075328/list-of-hex-keyboard-scan-codes-and-usb-hid-keyboard-documentation -

Thanks a lot; I post here my solution, not the simplest but works good: I use NirCmd.exe with customized keyboard shortcuts to modify anything:

nircmd.exe cmdshortcutkey "~$folder.desktop$" "Increase Brightness" "Ctrl+Alt+F10" changebrightness 10

When I hit a key on the matrix keyboard, the Arduino Micro sends "Ctrl+Alt+F10" to PC. NirCmd then translate this combination to "increase brightness". It can be used for almost any command such as extinct the monitor. Finally, a key on the matrix keyboard send "alt+tab" to switch between Processing, rear camera (webcam) and the GPS software. Project is complete. Have a nice week end.

Good solution! :)