OK I've read through the forums and thought I knew how to do this. I've edited the theme - documented.yaml file and commented out the emulators I don't use with a # sign. I've also edited the theme.yaml file in the theme folder I'm using (piworld) the same way. Buuuut the emulators keep showing up! What am I not doing or doing wrong? Thank you for the help!
@Dave - To hide emulators, you need to edit /home/pi/pimame/pimame-menu/config.yaml under each emulator listing you should have an option called 'visible'. Just set that to 'False' or 'No'