We do this same thing all the time. splitting between a studio and a 1BR. We have 2 kids who are now 11 and 13 (both girls) but we started doing it in 2009 when they were 4 and 6. On "change" day, we plan to be in a park until at least 4. Then, we plan dinner at our resort. Before we leave for the park in the morning, we drop our luggage off at Bell Services and tell them to hold it until we get back because we are changing rooms. When we get back, if the room isn't ready (never experienced this), we'd head to dinner. If it is, we grab the luggage and drop it off in the new room before heading to dinner. If there's time, I'd always start a load of laundry before dinner and then toss it in the dryer after dinner.
As far as packing goes, with the laundry facilities available, we can pack a LOT lighter. We take two rolling bags (both are small enough to qualify as carry-ons) in addition to a backpack for each of us. We pack the stuff for the first 2 days in one of the rolling bags and the rest in the other bag. This limits the amount of packing and re-packing that we need to do. Before the kids became "adults", we would add a dining plan for our first (studio) stay and then have groceries delivered for our 1BR stay with no dining plan.
Once we got the hang of it, we are now comfortable doing split stays between different resorts. It really lets us change things up an try new things. At 7 months, it is easier to find 2 night stays and 3 night stays than it is to find 5 consecutive nights in one room. This past October, we did something totally different...we split a week, starting with 5 nights at the BWV and then 2 nights at AKV. I don't typically like the longer stay on the front end, but I was pleasantly surprised. We had to pack up everything out of the BWV but when we moved to AKV, we didn't really unpack too much, making it much easier on check-out and go home day. It was much better than I expected. I won't intentionally split that way again, but I wouldn't completely rule it out either.