You can sysprep your system drive for another MB.
To avoid boot BSODs. To do this, go to C:\Windows\System32\Sysprep\sysprep.exe, check 'generalize', select 'OOBE' on drop down menu, and 'Shut down'.
When your drive boots off of your new MB, you'll get the 'out of box experience' screen, asking you to create new user account. Just call it anything and after that's done, you can log off and switch to your main user account.
Once you're logged in with your main account, you can safely proceed with deleting the newly made account in Control Panel > User Accounts applet
To clarify what sysprep does, it basicly gets rid of all platform specific data such as drivers and configuration files.
You should save all the stuff that you don't want to lose before you try any of this. Better safe than sorry.
Otherwise, just upgrading your CPU should not be problematic.