Yes - your crx would have to be re-registered as a 2 seater before any type of roll cage is installed. You could simply remove the seat but its best to have the car 're-registered' if you expect to drive on the street.

Im not 100% sure IF a 6pt cage would be allowed in VIC. I was told the only way a 6pt cage could be legally licensed in WA is IF its welded in and it has to go through the dash and run right beside the A-pillar.

As far as any cage goes it will have to be approved with your local RTA - if its engineered, custom made or bought as a bolt in. In terms of FIA or CAMS approval - you'd have to have the cage built to CAMS SPECS (refer to cams race handbook) - all specs are there.
CUSCO - i know someone here in Perth who runs this same type of cage 'safety21' in his 180sx and says he had no issues getting it approved.