[Analogus]

Thanks for your answer!
You seem to be a jack of all trades!

I for my part am not. I give up.

Installed terminal --> working.
Made script --> calling script in principle OK.
Copied altered sqsh-image onto the user area due to lack of space in other directories. Path: /mnt/us/test/
Copied script into the same directory to make things easier.

I presume, that the user-area is /mtn/us/

Script:

# You need to find the next available loop device:
nxt=$(losetup -f)
echo "$nxt"

# You have to use that loop device to translate your new file into a device
losetup /mnt/us/test/fonts.sqsh $nxt

# Then you have to mount the new device on top of the existing system at that mount point
mount -t squashfs $nxt /usr/java/lib/fonts

# Make cvm and its children let go of the old (now 'bottom') layer files
initctl stop cvm

# Get everything just stopped, re-started again
initctl start cvm

Script is running, but with error:
losetup: /mnt/us/test/fonts.sqsh: No such file or directory

Of course there IS this directory and the file, even beeing there with the shell, and script is able to be called up. It seems to be that the file is unable beeing mountet from the user-space.

Thanks for your help - I learned a couple of things.