If you read the NZTA site you do need a cert.
It used to be that you use could that loop hole, but the LTSA (now called NZTA) closed it. They set the rules. Not the department of labour!
You cannot ues a definition from one source to decide on a rule from another organisation!
read this:
http://www.lvvta.org.nz/CertThresholdSc ... il04V3.pdf
Then scroll to the bottom where it gives the definition of "OE" re certs/wofs.
Take specific note of:
"at the time it was built and certified by its manufacturer"
That line excudes parts of a different type fitted later. In this case TRD coilovers.
When I was selling TRD often a selling point was not needing a cert, then they added the above definition to the rules and slammed shut that loop hole.