sure you could – use scripts. you can load a game via the command line.
see https://github.com/libretro/RetroArch/wiki/Using-the-command-line
i don’t know what you mean by loading the ‘mame emulator’, though. you can load a game, or you could load a retroarch core and choose games through the interface, or you could edit your emulation station so it only has a mame menu. need more information.