Yes you can. The Currie 4 plug controller can be replaced with the 5 plug controller.
The extra plug with single yellow wire on the 5 plug controller is for a feature on the newer scooter versions which deactivates the motor when the battery charger is plugged into the scooter. The 5 plug controller will work exactly like the 4 plug controller when nothing is connected to the extra plug with single yellow wire.
I have a currie scooter with a 4 plug controller. Can I replace it with a 5 plug controller? I have attached pictures.