The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
Spray cans should not be used for repairing scratches on pre-painted sheeting.
If the scratch is obvious from 3 m, the sheeting should be replaced, if not then it should be left alone. Minor surface scratches become less noticeable as the coating weathers and are best left as they do not appreciably affect the corrosion inhibiting properties of the material.
Widespread damage caused by rough handling or an accident, however, should not be corrected by repainting, but the affected material should be replaced.