If you download Raspbian, FreeBSD, or any other disk image for the Raspberry PI, chances are you will want to make a few changes before burning it to your SD card. Loop mounting is the best way to do this, and it doesn’t have to be over-complicated.
The first step will be to install kpartx, which is available on any Debian-based linux distribution:
apt install kpartx
Create a Loop Mount
sudo kpartx -v a image.img
Create a Directory for the loop
mkdir -p PI sudo mount /dev/mapper/loop0p1 PI cd PI
Change loop0p1 for loop0p2 to access the ext4 file system. The partition loop0p1 will contain config.txt and the kernel images.
Go ahead and edit the contents as you wish.
Unmount the loop
cd .. sudo umount PI kpartx -v -d image.img
Burning your new image
dd if=image.img of=/dev/mmcblk0p1 status=progress