Another way to run CD-i (cdimono1) with MAME standalone (like MESS without Lr)
go in /opt/retropie/configs/cdimono1
open your emulators.cfg
add:
mame-CD-i= "/opt/retropie/emulators/mame/mame -c -autoframeskip cdimono1 -cdrm %ROM%"
To set your "Input (general)" and "Input(this Machine), follow step 10 and 11 of this Tutorial.
Tutorial: Handheld and Plug & Play systems with MAME
You can use .chd without specific MAME naming and without dummy file.