hi all i know this is post is pretty old but i had a similar problem what i did is make system specific .cfg for all the 2 button systems (Sega Master System.cfg Sega Game Gear.cfg and Sega SG-1000.cfg) and then open them in a text editor press control+f to search for text and type in remap. the second or maybe third line that contains remap should point to the dir where remaps are found. default should be ":\configs\remaps". i simply added a new dir so now it is ":\configs\remaps\sega". then save and close. next go create the new dir on the drive (open retroarch folder then configs folder then remaps folder and make a new folder named Sega.) next go back to the remaps folder and copy (DON'T CUT) the Genesis plus EX folder and paste it into the new Sega folder. Launch retroarch load one of the new system .cfg files then launch a game enter the quick menu go to controls and set up your new binds to use x a buttons instead of a and b buttons and then save the core remap config and you should be good to go. hope this helps someone out there. i imagine you could crate a second configs folder and do something similar using 2 seperate genesis plus ex.cfg files if the system specific cfg doesn't work for some reason in lauchbox my setup is in rocketlauncher and hs so im not very knowledgeable about launchbox but it worked like a charm for me. Happy gamiing alll!!!!
