With respect to aviation and aircraft, I usually just simply say that Engineers design airplanes and Technicians repair them.
Maintenance technicians have the authority to restore an aircraft to its certified configuration. They have no authority to repair or modify the aircraft in a manner that is not contained in the maintenance manual or on other approved documentation.
An Aeronautical engineer can take different roles. Some are committed to design, others to certification. (Some are both)
Engineers can design aircraft, repairs and modifications. Appropriately delegated engineers (or other such delegated persons) can approve said designs, repairs and modifications.