Mark a VM as "ephemeral" / read only

I have a workflow where I repeatedly test installing and uninstalling software on macOS. This means I very often clone and delete macOS VMs. I currently create a "Pristine" image that I then copy and boot.

This works well, but is really annoying when I accidentally boot the Pristine copy and mess it up.

I would like it very much if I could tick a box that said "always clone this VM before booting" or whatever, that makes it hard to accidentally ruin the pristine copy. It would also be fine if it did let me boot the VM, but then the changes were destroyed after I shut it down.