To begin with, it's definitely not easy to install SteamOS in VirtualBox. Valve clearly didn't intend for you to do this; you can't just mount an ISO and install it, like a normal Linux distro.

VirtualBox Snapshots allow point-in-time recovery of a virtual machine and can be used to restore the machine, Learn how to use Snapshots in VirtualBox.

Second, VirtualBox allows any ISO to be mounted as though it was native by using the Virtual Media Manager.