i think it is very hard these days as most places like Vic Roads etc will want a vin #. if that Vin # does not meet ADR's (aussie design rules) then its a no go unless you make it meet all that criteria.
in 1987 i wanted to rego my CR250, so i made up a full lighting loom, indicators, lights, horn etc etc mudflap, chain guard, universal tyre, all sorts of shit took it to an engineer for cetification and was knocked back for things like the master cylinder for the front brake had to be marked "clean before opening" so i did this and other things and was knocked back again for more shit.
i gave up, took it to an outer metro cop shop and success. kept the full rego up for 10 + years on that bike then dropped it back to Victorian Recreational Rego when that came in.
this was 22 year ago. i reckon it would be impossible now. Maybe someone else know an easier way.
Buy the KTM 300EXC Utsman, you won't be dissapointed. i have both and the KTM is much better bike in the bush, i would hate to ride the CR500 on the trail, its all wrong (gear ratios, power spread, ergos, suspension etc) unless you are MR physco and use the throttle as a light switch.