Try with tincore keymapper. It allows you to change keycode for any key. It's a bit tricky to use though, but better than editing kl files. L3 and r3 in Android are generally Button_thumbl and button_thumbr, instead of button of button_l3 and r3 which are not generally used in any joystick driver. If you re-edit the kl files try with button_thumbl and button_thumbr, and are members to set correct permissions for the file.