It has been done... N20 is a bit more expensive than C02 but with similar temp properties when released, the down side would be when you wanted more power, you find it is low because you've been shifting. If this is a race bike, ensure your organization allows it...
N20 and C02 can both be transferred from one bottle to another, without a pump.... empty in ice, full in sun... pressure difference will move liquid one the the other....