This isn’t some rigid DRM scheme either; you could ask Fulvio for a new activation explaining what you’re doing.
If it’s VMware you can change MAC addresses of virtual NICs to a limited extent. It will tell you if the address you supplied is good to use or not; some dynamic MAC addresses can’t transfer to another VM.
Or, just install the new Zeroshell on top of the old one, or change the ISO image it uses, and keep the remaining VM settings unchanged. You can restore profile backups from older ZS versions to newer ones. Just remember to take a profile backup first.