if you are flying commercially under part 107 then each drone in your fleet will need its own individual reg number
if on the other hand you are only a hobbyist flyer then the number can be applied to all your drones ,i dont believe that an individual 107 registered number is transferable ,you would have to check with the FAA
It's a LOT easier to just register the new aircraft. While there is a potential to transfer an Aircraft Registration it's a tedious task and costs the same as just registering the new one. It's so much easier to CANCEL the current registration (FAA Drone Zone) and then register the new one IF you are replacing an aircraft. IF just adding another to your fleet no need to cancel just register the new one.