I've transfered my current Win7 Home Premium 64-bit OEM to several different upgrades, every one including a different mainboard and CPU. Each time it validated without me having to do anything.
If you do happen to have a problem, call the special number and explain. They'll approve it.
And as long as you're as careful pulling the CPU out as you were putting it in, there shouldn't be a problem. The easiest way is to have both boards next to each other. Take the CPU out of one and put it right into the other.