uci set attendedsysupgrade.owut=owut
uci set attendedsysupgrade.owut.init_script=/etc/owut.d/custom-init.sh
uci set attendedsysupgrade.owut.pre_install=/etc/owut.d/take-backup-to-extroot.sh
uci commit
uci show attendedsysupgrade.owut

# Verify that it's in owut's config
owut blob

# chmod +x both of them
chmod +x /etc/owut.d/custom-init.sh
chmod +x /etc/owut.d/take-backup-to-extroot.sh