Just to clarify what you trying to do, you want to duplicate an event + all of the registrations on that event? May I ask what the use case for that is?
We don’t have an option to duplicate an event + its registrations but we do have the option to duplicate an event. Edit the event and click the ‘Duplicate Event’ button next to the permalink at the top of the page.
The barcode is generated on the fly using unique values within the registration, even if you ‘duplicated’ the registrations they would need to have the unique values mentioned otherwise EE wouldn’t know which specific registration the barcode is for when scanned. So technically not duplicates but copied registrations with their own unique values.