No. It is NOT possible.
You can only designate the car class, can NOT choose a model, nor further car details etc., due to class specification reservation.
However, car models can be specified for Nissan Rent A Car.
Nissan;
Car model specification is possible when you book.(there is only 1 model car per 1 class).
*There is a case another model car is offered including an upgrade due to irresistable reasons.