There are examples of Decepticons like "Jetfire" and "Wheelie" that turned and changed sides to the Autobots. Jetfire in Transformers: Revenge of the Fallen is quoted:
It's a choice. It's an intensely personal decision. So much negativity... Who wants to live a life filled with hate?
But has there been instances of Autobots who have changed sides and remained Decepticons?