I have a hidden admin CIFS Share configured for the underlying volume, with the CIFS permissions locked down to a user or one group on the appliance.
We dont use SMVI currently, but have snaps enabled at the volume level, so if we really wished to restore a previous version of a VM, we can using the previous versions tab, within the CIFS Share properties. This is just an easier method that entering the details at the CLI.
If you really want to lock it down, then no. I also agree, I wouldnt reccommend editing the VMX files directly.
Martin