We end up splitting our stays often as family joins us/leaves us we need different size rooms.
Disney doesn't transfer "people" and you can't take luggage on the bus but bell services will transfer your bags to the new resort for you.
We let bell services transfer our bags, head to a park for the day and then check into the new resort after check in time. Done it many times and for the cost of a tip - (at both ends!) we find it very convenient.
This works well for us and since the room at the new resort most likely won't be ready in the am, you would have to store your bags at the new resort (and tip) anyway.