You can with a sufficient window (I can't remember what it is in-game right now).
But, one thing you can't do presently is change to a model that didn't exist at the time you placed your order. While, yes, this occassionally happens in reality (sometimes the manufacturers even try to get them to do it in order to phase out the earlier model sooner and cut some costs), there are problems with doing that in-game. We have the benefit of knowing the future. We know for a fact that there are superior versions of a model coming out at later dates. We could abuse that knowledge, order lots of planes of a lesser model, then upgrade it later on when our prophecy inevitably comes true.