at this moment i can provide one solution
ubuntu or other linux shell
# change bootmode to SPI / for next oowow boot up
# sd card must be empty
i2cset -f -y 6 0x18 0x20 0
# may be need some system preparation like unmounts ....
init 1
umount /boot
mount -o remount,ro /
#
# reboot via mcu
i2cset -f -y 6 0x18 0x91 1
oowow shell
# some custom tasks
# ...
# and last steps is change bootmode to emmc back
i2cset -f -y 6 0x18 0x20 1
# reboot back to emmc os
reboot
ssh oowow usage example - back to emmc OS
ssh root@vim4-xxxxx "i2cset -f -y 6 0x18 0x20 1 ; reboot"