Great comment by Wheelbender!
There is a vendor in your country that sells the 200w HT(gas) kits, I think it is Rocksolid.
Also, since there are more than a few of you guys from Down under here, there are conversations in the archives to search for.
I had a similar issue in my state where anything with a motor is considered a motor vehicle.
I bought a moped which only required tags and converted my bike into it.
It still looks like a bike, very quiet, motor hidden, ridden sensibly, always with a helmet, and has a cycle license plate on back, to avoid hassles.
I have actually gotten scolded by a car driver for not being on the bike path going around a local park.
At least you CAN motorize, the 200w is measured at the rear tire, I understand. The HP at the engine would be more.
And the engine can be de-restricted for more umph, but still has the paperwork showing 200w.
Of course, if you are flying down the road attracting attention, you likely will get the attention you do not want.