In Morty 2.3, you must know ahead of time where the images will be written to or the installation fails. The default --ondisk sda works fine on USB drives but fails on MMC/SD cards for example. I suppose partition /dev/disk/by-uuid/* will be fine too, but there will be a hard requirement on using udev and race conditions to set up the device node links. PARTUUID does not rely on udev.
This seems to be a duplicate. Please, have a look at the bug 11525 and add your requirements there. Thanks. *** This bug has been marked as a duplicate of bug 11525 ***