Maybe...
This video says no
https://www.youtube.com/watch?v=JZn_hSlT0zk
But...
It's likely that since you are changing the board your win 7 key won't even work with your new board. Since the Keys get tied to your system.
the oem microsoft license agreement says:
“An upgrade of the motherboard is considered to result in a “new personal computer” to which Microsoft® OEM operating system software cannot be transferred from another computer. If the motherboard is upgraded or replaced for reasons other than a defect, then a new computer has been created and the license of new operating system software is required.”
Also (IDK a lot about AMD) if I am not mistaken AM3 to AM3+ is a change in architecture. So I personally say yes you would have to.
As for a CPU change no, you don't. You remove it from device manager and update drivers.
so Maybe....
I don't see that as a reason for cancelling an upgrade. Is installing windows really that troublesome? I would upgrade windows x:
(lel windows 7 :lol
Edit: actually AM3+ doesnt seem like a change in architecture to me since its compatible with AM3, so id say most likely you don't have to.