1. Install required packages (requires admin rights):
   sudo apt install wget
2. Download the aml_image_v2_packer utility file to the current directory:
   wget -nc http://update.jethome.ru/tools/aml_image_v2_packer
3. Make file executable:
   chmod +x ./aml_image_v2_packer
4. Create a directory for unpacking the out image and a directory for mounting the rootfs partition mount:
   mkdir -pv out mount
5. Unpack image to out directory:
   ./aml_image_v2_packer -d Armbian_20.08_Arm-64_focal_current_5.7.16_j80.img out
6. Mount the rootfs partition to the mount directory (requires admin rights):
   sudo mount -v -o loop,rw out/data.PARTITION mount/
7. Modify rootfs (requires admin rights):
   example 1:
   echo test_parameter=777 | sudo tee mount /etc/test.conf
   example 2:
   touch test_file
sudo cp -v test_file mount /usr/lib/firmware/
8. Unmount the rootfs partition (requires admin rights):
   sudo umount mount/
9. Pack the out directory with the modified rootfs partition into a new image:
   ./aml_image_v2_packer -r out/image.cfg out Armbian_20.08_Arm-64_focal_current_5.7.16_j80_REPACKED.img
10. Remove out and mount directories:
    rm -rf out mount

For J100 use file Armbian_20.08_Arm-64_focal_current_5.7.16_j100.img