Ive done two split stays this year. January we split between WL and AKL and in May I stayed two nights at POP. rented DVC points at BWV for five nights, then went back to POP for a final two nights.
WDW makes it easy. The morning you're ready to change, just call bell services and tell them where you want your luggage to go. At a deluxe or moderate you have to be in the room for them to pick it up, however at a value you just leave the luggage in the room and go off to the parks. In my case I feel I'll have a better chance of getting the room I want at the new resort if I check in early, so after calling bell services to come get my luggage, I catch an early bus to the nearest park, then catch another bus to the new resort and check in. If your new room is ready you can check it out, if it's not they'll give you a room key and a number to call back later for your room number. Then you just go off to the parks. If you're in a value resort your luggage will be waiting for you in your room that night, if you're in a deluxe you'll have to either stop by bell services or else call when you get in your room and they'll bring your luggage right up. I'll be doing another split stay in Dec and can't wait. It's like having two vacations in one. I love switching resorts.