Well, with Luma you can change the System Version string in settings to say whatever you want. But aside from that, I think you're talking about trying to customize or change the overall operating system of the 3DS.
I think I've seen one instance where somebody tried to do this, but then closed the project. I think it was pretty dangerous with a risk of bricking, at least at the time.
Other than that, I think you're out of luck. You can try Sunshell or Cyanogen3DS, but I'm not sure that either can launch commercial games, and I think they haven't been updated in a long time.