CEC Button remapping (Disable skipping)

Hello everyone,

I am running OSMC on a Raspberry 3 connected to my Samsung TV via HDMI.

As my TV somehow does not send “volume up” or “volume down” commands via CEC I would like to remap the “left” and “right” buttons to change the volume when listening to music in fullscreen mode.
I have already downloaded the Keymap editor add-on, but I was not able to disable the default mapping for the “left” and “right” keys, which is skipping forward and backwards when listening to music.
Does anyone know how I can disable skipping or how to change it to different buttons?

Thanks in advance and best regards Thomas