G010SA is different from our modules.
My guess is the G-010S-A's folder containing etc must be mounted as read-only. It is still possible to find a way around it.
That's what I would do. There are probably automated scripts for this task.
- Examine the G-010S-A firmware (6291456 bytes) with binwalk.
- Use dd to extract the squash filesystem from the firmware.
- Unpack the squash filesystem using the unsquashfs.
- Make changes to omcid.sh
- Re-pack the filesystem using mksquashfs sqdir/ sqsh.bin -all-root -b 262144 -comp xz
- Assemble the firmware parts cat(uImage+LZMA+Squashfs)
- If the modified firmware is less than 6291456 bytes, append some zeros (dd if=/dev/zero, cat)