You can register a car in the 'commercial'  class if all the seats behind the driver are removed. Instead of the seats, you must install a permanent box or permanent rack to carry cargo.
Alright. And if I remove the speed governor of my moped?
Then you must notify DMV and register the moped or motorcycle in the appropriate class.
I love to tinker on all kinds of vehicles, I'm an auto-mechanic. So which modifications would change a registration from commercial to passenger class?