tip: if you have qemu-arm-static installed on your host system and the sdcard mounted at /mnt/tmp (fill in different path to taste) you can "enter" the image with:
systemd-nspawn --bind-ro=/usr/bin/qemu-arm-static --tmpfs=/run/lock -M pyra -a -D /mnt/tmp
now you can just change the root password with "passwd", or create new user accounts. even installing packages using apt-get works fine