Nick you see people pull pre market open orders all the time. I have seen a 200,000 and even 500,000 bid pulled on other shares just before market, sneaky moves I suspect to push bids up.
Yes you can change them, it is very common. If you refresh the screen you can see pre open price change quite a bit depending on the bids that are in (and how badly people want to sell or buy).
Good luck.
