try add a new disk with the same configuration of your existent disk and remove blank disk and copy your disk with data on the same place. i work with raw files one time i do that without any problem to replace a backup disk file on tests. To everyting with your machine stoped.
Example: Location of pysical file:
zulu:/var/lib/vz/images/<<VMID>>#
vm-<<VMID>>-disk-<<DISKID>>.raw
Note i do it with disks with data i don´t do that with system disks. i use separate files for system, swap and data.