Yesterday I changed the rear seat which was very easy to do. The hardest part was to remove the isofix-bar and the middle bolt from the backrest hinge. You have to carefully open them and spray some penetrating oil to the threads because the threads are fully exposed in underside of the car so they might be rusty.
Passenger seat was relatively easy to swap, I changed the seat belt pretensioner because the connectors are different in Ph.1 and Ph.2. I also had heated seats in Ph.2 seats but not in Ph.1 so I had to cut the wires from the same connector which has the seat belt pretensioner cables, not a big deal. The side airbag connectors are totally different so I had to cut the connector from my Ph.2 seat and solder it to the Ph.1 seat harness. Then I noticed that 3dr seat rails do not move back and forth as much as 5dr rails so I swap the rails (only five lugnuts) from my old seat and disconnected the cable which allows rear seat access in 3dr cars.
Driver's seat I couldn't swap just yet, because I need to make a hole in seat's frame for the seat position sensor which is in my Ph.2 seat but not in Ph.1 seat. I will take the seat to a friend of mine which has the proper tools to make the hole. Then I can install my 5dr seat rail also to the driver's seat.
So for me, they were not plug-and-play install but when I'm finished the extra work will be totally worth it.