Quick WIN7 OEM question

Yes.

After hardware changes, you may need to call MS to activate...

Yes. You can reinstall the OEM copy on the original system it came with as many times as you want to or need to. As r-sky said though, the online activation may not work, and you would have to call Microsoft. The phone activation process is really easy, completely automated (unless there is a problem with the info you provide the system), and only takes about 5-6 minutes.

You may need to call them up a couple of times to get through to a real person though, when I've had to call them in the past it has a habit of hanging up on you before getting to that point.

You don't need to talk to a real person in this situation. The automated system works very well.

Backup and restore Windows 7 activation application.

http://www.recipester.org/Recipe:Backup_and_Restore_Win...