[Q]Remap hardware buttons without additional programs.Sammy 4.3

I would like to know how to remap POWER button, VOLUME_DOWN button and BACK button to different actions.
In details i want to use long press action for POWER button as camera shutter, VOLUME_DOWN button as POWER menu, and BACK button to kill foreground applications.

I used to manage that with Xposed Installer and Xposed Additions as the pictures show.
http ://thanosdi.info/tempfolder/overview.png
http ://thanosdi.info/tempfolder/1.png
http ://thanosdi.info/tempfolder/2.png
http ://thanosdi.info/tempfolder/3.png

but i would like to know if i can manually do that from the system/usr/keylayout files so i dont have to install both of these programs just for hardware remapping.


My rom is Samsung TouchWiz 4.3 rooted.Thanks in advanced.

Shameless bump