We can directly copy the vdi for new VirtualBox vms.but the UUID will be the same as old one. so we need to change the UUID
$VBoxManage internalcommands setvdiuuid /opt/vms/c52_master.vdi
VirtualBox Command Line Management Interface Version 3.0.10
(C) 2005-2009 Sun Microsystems, Inc.
All rights reserved.
UUID changed to: aa742648-c3f4-408f-bde8-827dadff5cca
if in Windows, find the installation directory of Virtualbox and then run the VBoxManager.exe command in cmd lines.