Please share the details for adding Squashfs-tools addon for make changes to the read-only part of LibreELEC.
I hope this helps… It’s not a tool but will show you how to mount, unpack, and repack squashfs using linux.
when creating a squashfs, when you come to repack the image, make sure compression is set to lzo (-comp lzo).
https://sites.google.com/site/andreierdei/openelec-addons/squashfs-howto