So I could use my windows 7 32 bit premium key and upgrade to 64 bit windows 7?
I have done exactly that. I did the reverse explicitly so I could run civ 2.42 which only runs on 32 bit.
No problem reactivating.
I did this on a laptop with a oem product key.
The motherboard is still the same, so it does not violate the oem limitation.
I used a windows 7 32 bit upgrade dvd.
I think actually all of the windows dvd's are exactly the same, differing in 32 or 64 bit versions.
It is the activation key that unlocks the different options.