My preferred workflow is to install a system into a VM and make the snapshot there. Then I can upgrade the VM any time I want and make a new iso. It doesn't have to download the whole system every time.

Then, if I want to use a live, read-only system, I just boot the iso file inside a VM and use that. Then I don't have to reboot the computer to switch to read-only. When the VM shuts down, everything from that session is gone.

found several forum-links pointing to fsmithred's topic: Make a live-CD with live-sdk

• While not an answer to the immediate question, it is one possible solution to the problem at hand.

continuing...

Requesting help in considering that with this use-case:

• booting from DEVUAN desktop-live .ISO often

• up to several concurrent instances, several times per day

• with zero persistence

and keeping devuan-security in mind, that it might be good to "not wait" for next .ISO release before updating packages.
Also, I suggest that it would "not be sane" to burn up bandwidth by performing apt upgrade upon each boot.

That leads me to believe that several of you must already have a routine for: upgrading the DEVUAN desktop-live .ISO

So let us say that the upgrade will be done from "inside" the booted .ISO and that we expect the high-level steps to include:

• Burn to DVD the latest DEVUAN desktop-live .ISO file. (or write it to USB) https://www.devuan.org/get-devuan

• Boot computer (or virtual-machine) from this new DEVUAN desktop-live media.

• If not already connected, insert some storage-media with enough free space for a copy of the new filesystem and an .ISO file.

• Connect to network (INTERNET)

• To update the operating-system, open Terminal Emulator and run:

  sudo apt -y update && sudo apt -y upgrade

• Optionally pause here to make more changes: add/remove packages; update settings to personal-preferences, e.g. browser-configuration; add files; etc.

• Then to create an .ISO of this improved state of the operating-system, open Terminal Emulator and run:

  sudo refractasnapshot

• Burn to DVD the freshly-upgraded DEVUAN desktop-live .ISO file. (or write it to USB)

(I've spent a bit of time trying the above, and have learned that it is not quite as simple as stated, e.g. issues with updating kernel and initramfs; minor-changes required in /etc/refractsnapshot.conf; ...???...)

So I ask those in-the-know, if you could please share the complete steps.  Or bring forward any helpful hints.  Thanking you in advance.

Separately, if there is any how-to info out there on doing automated builds of the desktop-live .ISO, please share those links here as well.