I don't know any BOINC configuration file editing tricks, but if you reinstall the OS and keep the same computer name, it will be a new device. I've done that a few times on a few computers (for various reasons) and each time it's a new device.

What elements changed... CPU? Renaming the host does not work as WCG keeps track of about 5 parts, CPU, OS, IP and then tries to match these with a prior known device. See Wiki: http://boinc.berkeley.edu/wiki/Host_identification_and_merging **

A rather novel need to actually want a new device registration: Alienation starts with detaching WCG from client ["Remove" in 6.12 new speak], stop the Core Client service and delete a few key files (all client_state and those that has WCG in the name + the project dir) from the Data_dir does go a long way of forcing the hand. After, start up core client service (boot for instance), then "Attach" WCG again to client ["Add" in 6.12 new speak].

** The <suppress_net_info> trick from the wiki may not work. Certainly I've found that renaming the host does not change the host ID number.