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

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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.