Installing Ubuntu will name the device Ubuntu. You can change that in the 'hostname' file, and maybe too in 'hosts' on your system. What is transmitted to WCG is what the system is known at on your local network. Change the name, boot and it will transmit the new name.

If there was a clean install, there's hardly a chance WCG would recognize the device as an existing one, though the hardware is part of the 'hello old friend' identification process.

Oh, and yes you can have multiple hosts with the same name in device manager. There's though an underlying unique device ID, 7 digits now. But how this could be... IP conflict on your network? Cloning clients also gives issues. The unique ID assigned by WCG is stored on the client and used when reconnecting. Imagine two hosts saying they're the same 'me'... work-assignment becomes a mess, so much so that if one hooks up and gives an update of work assigned and it not matching, work will be dumped. [Each client maintains a last connected counter, so if it tells device A connected at hh:mm:ss for Nth time, and the duplicate but device B comes back with a different last connected counter hh:mm:ss for Nth time, both in the end are considered out of step.]

Edit: In effect, even if you have a full backup of BOINC, kept it running, then restore, the client counters will be backward and on reconnect the 'old' work status is dumped... no complicated inventory taking.