Yes you can do that - its likely to be fairly expensive for the Sequoia Lodge though (I noticed on Expedia that room only for the Santa Fe and Cheyenne for winter dates can be as little as £64 per room per night, but the Sequoia Lodge is double that price).
You can either phone Disney and get them to add the night (without park tickets) to your package, or you can book the room only through Expedia etc and then call the Sequoia Lodge a few days before you arrive, to explain that you have the extra night, give them the booking numbers, and can they arrange to have you stay in the same room for the entire duration of your stay.