so if you put the ‘rotate’ config line in the main /opt/retropie/configs/mame-libretro/retroarch.cfg it applies it in mame2010 and 2003?
assuming that’s true, it seems like you’ve you’ve ruled out everything exept that mame2010 just isn’t reading the override cfg files. i don’t think this is a retroarch/core issue, as overrides are handled centrally by retroarch (i think) – if that wasn’t working it wouldn’t work in 2003 either. i think it must be something to do with how mame2010 is being launched by retropie (perhaps it’s not got the correct target directory or something like that). i think at this point it’s best logged as an issue here: https://github.com/RetroPie/RetroPie-Setup/issues