You may get lucky, you may not...
The RTA guy that came to my house and inspected my trailer before they gave me a vin number was very specific;
"When you apply for a new vin number for a home made trailer in NSW we personally inspect them to make sure they are actually home made and not re-birthed."
There was no grey area with that guy, if my trailer wasn't clearly home made I'm positive he would have had an issue.
Others in NSW may have had different experiences registering their home made trailers, but that was mine.