In the most technical of the legal technicalities, it is completely illegal. (huh?)

Basically, four seat CRX's were not crash tested for the American market, therefor it is not legal to carry more then two front seat passengers in any CRX in the US, whether it has back seats installed or not. 99.99% of cops will have no idea though, and will not ticket you... but if you crash the car with someone in the back seat, you're just begging to get your ass sued.