Hi,
Regsitration code is one time activity after u install application.
If you do any of the following you must re-license the software with a new registration code:
• Reinstall the operating system on the same hardware
• Install a different operating system on the same hardware
• Add or remove certain hardware (such as an NIC card)
• Change the machine name
• Perform a major upgrade
http://www.cisco.com/c/dam/en/us/td/docs/voice_ip_comm/cucmac/cuacs/10_5_1/install_admin_guide/CUACS1051GUIDE.pdf
So, try changing the machine name on same HW to get new Regsitration code.This is what I think.
regds,
aman