Hello,
if both machines are in a cluster, you cold migrate the VMs. Otherwise you could create a new VM and replace the disk file (never tried that). I once created a qcow file and imported it as a new image and created a template for it. AFAIK there is no export/import function. Copying the datastore might fail - I assume, that the database is not updated with records for the VM.
Regards,
marc.