it is indeed possible. people even do it with their prado's. but you will completely screw up the engine in a year's time. cng usually messes with the MAF sensors and since its a harrier, it ought to have a lot of more complicated sensors installed, which will end up becoming weak. moreover, the ECU will always be confused and you will experience several complications, such as the AC not working at low rpm's or the injectors not providing enough gas for combustion to the engine. and once you decide to sell it, noone will want to buy a harrier with CNG installed in it. generally people who can afford high end cars can afford to put HOBC in them.
on the other hand, if you intend to sell your car after using it for 6 months, and are not concerned the engine's life or performance decrease that will definately occur in a year's time, then by all means, go ahead.
good luck with the project.