A556 set is wrong, A945S is correct... maybe refills?
The A556S sold everywhere has incorrect lengths of 600 mm and 400 mm. It seems the correct set is A945S which contains 650 mm and 400 mm, however as they seem to be available from German sellers only I wonder if they could be for left hand drive cars? Aerotwins aren't symmetrical like classic arms as they form a spoiler.
I've just check, the kind of mount in these for the Seat seem to be relatively easy to rotate, you need plastic bar to prise both sides a bit and then you can press it back rotated.
I have to return A4556S I received... And I think I buy only rubber replacements for OEMs and they seem pretty rugged mechanically and the rubbers seem to be very easy to replace.