You do not need to do that if you need the changes for a running system.
We have used overlayfs with the RO squashfs and a RW folder on the data partition.
This creates a “writable” rootfs without modifying the original squash file.
Your modifications will be kept on the data partition and “merged” with the squash file during boot (our own initramfs).
Ok thank you Gé for the advice.
The overlayfs was not running on an upgraded volumio version (?!)
Since i played with last image file and sd cards, overlayfs is available and very usefull
Are you sure it was not running. Perhaps you overlooked something? Without overlayfs, Volumio would not even start.
That said, we had reports in the past from older versions with the 3rd partition not resizing properly.
Overlayfs should made updates transparent, unless they were substantial and used more space than was available because of the failing resize.