No, they did not need to design a new aeroplane. They redesigned the fuel tanks on the existing A350-900ULR and certify it as A350-1000ULR, that's all.
It turned into 5 days. After realising I'd forgotten to change the block size to 4096 and it was horribly slow, I yanked the drive out, tried with my utility to set it to 4096 bytes and failed, found another utility that did the job, put the drive back in, wait 3 days for it to rebuild the array without the new disk, and then another two days to add the disk back in. Sigh.
Still, with 4k block sizes, it goes like shit off a shovel.
White supremacists on the rise in the US.
Never forget, there were people already in the US when they first arrived.
White supremacists stole their lands.