you should be able to do either, i Have memory seats in my VY berlina, I Had Bought a set of front seats from a VY calais
I removed the Foams from the frames and refitted my foams and trim onto the calais frames, wasn't real difficult, but Holden did change the seat frames during production a few times, 3 to be exact that ive found, we have 3 VY berlinas in the family 2 of them are 2003 models and mine is a 2004,
the major change i've noticed is 2003 have the same seat setup as VX, and my 2004 has the same as VZ, the easiest way that you can tell is the Map pocket on the rear part of the seat wraps around the sides of the seat on the 2002-2003 and on the later VY models it doesnt, the other change i've seen is on some early 2002-2003 seats they dont have a seat belt warning light wire, my sisters 2003 berlina wagon has one, but her husbands 2003 berlina sedan doesnt , both have the early VX type seat assembly
you will need to find a seat of seats that have the same map pocket setup as yours so you can just swap your seat foams onto the calais frames, and also keep in mind if your car has side impact airbags, which are mounted in the seats.
you wont get the priority key setup the calais has which adjusts the seats, side mirrors and radio settings to the user of that keys preference as that requires a BCM change, but the seat memory module is only about 4 or 5 wires to hookup by memory you will also need the plug from the VY you get the seats from as it is different and has the additional wires
