I believe standard at Princeville is 12-16K depending on season. I don't believe it is possible to switch a reservation from cash to points. I'm pretty sure you have to cancel and re-book and you're not guaranteed that the room you had booked will be available, even if you do it all at the same time. At least, that's how others (including Lurker) have explained it.

If your two bookings are for the same level of room (i.e. partial ocean view), you should be able to stay in the same room as they should just combine your reservations upon check-in. I've done that a few times at other hotels.
If, however, you book two different levels of rooms, you may be switching in the middle of your stay.