here is an overview with the partnumbers. The pads are the same, but also the calipers itself have different partnumbers not only the carriers.
But anyway I would like to give you the advice to be carefull with the rear brakes, as they are essential for stability during braking. If the brake balance isn´t O.K. anymore and especially if it is shifted to the rear, this might lead to dangerous situations, even with ESP and ABS.
I have a 2005 1.6 Grandtour with the 270mm discs at rear, and I always suffer from rust and corosion at the rear discs, which is claimed at nearly every mot (TÜV in Germany), so this is another reason to stay with the original ones.
I made the conversion to 300mm at the front with my Grandtour. As I have the older Version with the Bosch calipers (till 11/2005), it was clear that it was only necessary to get the other carriers and discs, ant that´s it.