Perhaps everyone has not thought through Grizzly's legal interpretation:
I am a CPL holder. Can I fly as PIC or instructor on a 1900 under SA Law?
Yes you can, provided you comply with the limitations set out in the AFM.
I am a named pilot (PIC) on 1900 ZS-XYZ's insurance but I have a CPL. Has the insurance company broken the law?
No, they haven't since you may legally fly the aircraft as PIC if you comply with the limitations in the AFM.
Hey, there might be other, more esoteric, interpretations of the same law but the one outlined above is a likely candidate for adoption by a court as it is straightforward and logical.