If your motherboard can handle the i7, it will be fine with the i3, Windows 'may' ask you to reactivate as hardware changed, but I doubt it, and even that you should only need your Windows Product Key
If your motherboard can handle the i7, it will be fine with the i3, Windows 'may' ask you to reactivate as hardware changed, but I doubt it, and even that you should only need your Windows Product Key