so nice!! I cant wait to see it finished and hope you will share it then too! So far I have tweaked a neogeo theme from here from ruckage but I think i much prefer this style to go with the aes (i think the red with white stripes mvs is more suited for the arcade machine)
With your help, I finally tested this (so far with one game each system, but there should be no reason why the other games don't work as intended now) successfully. But there is a mistake in your posting.
modify the system's retroarch.cfg and add
core_options_file = `/opt/retropie/configs/<SYSTEM>/retroarch-core-options.cfg`
The emulator does not seem to read from this setting, but there is already an existing setting for this file. Instead of core_options_file look for core_options_path. This worked for me. Anyway, thousands of thanks, as this was the last riddle in the Neo Geo mystery to me and I tried to figure this out since month! I am really happy now.
I do want to do the soft links again for another ROM related project in the future. So I would love to remove that copying and pasting step. The project would be simply to make a separate system for GB and GBC games that have two player game link support between two identical games with, obviously, lr-tgbdual as the emulator. Of course, this being GB and GBC, the identical copies wouldn't be as bad space-wise as Neo Geo was.