I replaced the built-in 1.5TB hard disk with a new 2TB harddisk. The partition
content was copied with rsync from the old paritions to the new partitions.
I adjusted all relevant settings in /etc/fstab, /etc/grub.conf,
/etc/default/grub_installdevice, /boot/grub2/device.map,
/etc/sysconfig/bootloader, /etc/default/grub to match the LABEL and
/dev/disk/by-* of the new 2TB disk.

Then I started yast2 to let it update /boot/grub2/grub.cfg, /boot/grub2/grubenv
and to reinstall the bootloader on the 13.1 parition. 

But all it does is to redo grub.cfg and grubenv. It did not install the
bootloader into the root partition. As a result chainloading the given root
partition fails.

Maybe I just missed the knob to reinstall grub2, instead of just regenerating
its runtime config files?

Will try again with the Factory partition now.