Three options I can think of:
1/ Use Resource -> Import/Export device to export your list of nodes as CSV, then import it back to the rebuilt system. Not perfect, but isn't too bad.
2/ Just rediscover the systems on the rebuilt system. Not that hard using auto-discovery tools, assuming they don't have 15 different SNMP strings.
3/ Probably the best option - just ask a friendly HP contact to generate an eval license. It's usually not very difficult to get a new time-limited license generated, and then you don't need to change any config. In my experience, HP has been quite happy to provide extended eval licenses to potential customers (after all, they want you to like it and buy it!)