The convenient thing would be for Launchbox to automatically disconnect hiscore uploads if it detects that cheats are enabled in the MAME I'm launching. That's why I'm talking about two different versions of MAME. In fact, I have one called Arcade64, which is the one I use to do all my roms' cheats, BUT, I have to exit Launchbox and use its own GUI every time I want to test with that version, or go to the Launchbox menu and turn off the hi-scores upload option, which is not very convenient.
Maybe one day they will make it easier.
Edit: Another less laborious option for Launchbox developers would be to put an easily accessible button to activate/deactivate the hi-scores upload option, and not have to enter the menu each time, with the drawback that you don't know if you left it activated or deactivated last time. If the button were visible from the main window, you would know what state the option is in before launching any game.