or if there is such a thing
CASA will tell you, there is no such thing as a low flying rating. The Ag and Mustering ratings both have (identical) sections of their syllabii which cover low flying, and this section will generally be referred to by CASA when issuing an authority to low fly.
eg, the requirements in CAO's for fire fighting require a helicopter pilot engaged in water bombing to have completed the ag endorsement low flying syllabus.