I did think of doing that, but we've got the disney express booked for arriving at 6pm on the 3rd December.
If we change our booking to arriving on the 2nd and we don't turn up until the early evening of the 3rd, do you think that they might cancel our booking ?
When we last went to WDW we were a day late. Not on purpose but there was a nationwide grounding of a certain type of plane which affected all airlines and of course we arrived in LAX from OZ, headed to AA to get our DFW to Orlando boarding passes (we had our boarding passes from LAX to DFW from Qantas, they said for some reason we can't check you in for the DFW/Orlando let, ah no kidding, thats because the flight is cancelled

) anyway so we are at LAX at 7.30am and had the AA staff trying to get us to Orlando. All flights were full for the next 5 days, we could get on the plane to DFW, but then we would also be stuck there for at least a week so they got on the the job of finding a way to get us to Orlando ASAP. As there were literally millions (I think 3 million was the number) of people were displaced due to this grounding of I think an MD80 on all airlines, there was chaos in all airports around the US, so we were soooo lucky that AA looked after us as well as they did. I was almost in tears as I said we can't be stuck for 5 days, we have paid for our WDW accommodation.
So we had 4 staff members on 4 computers (thank goodness we were flying first class otherwise we would have joined this massive queue for hours just to be served) and they found a flight out of LAX to New York, then got us on a Delta flight from JFK to Orlando. AA put us up at the airport hilton for the day and provided us with lunch and dinner so they really looked after us. Our flight didn't end up leaving LAX until about 1am as it was delayed and delayed and delayed (it was supposed to leave at about 8pm). We got to JFK late obviously and our flight to Orlando was about to leave. We ran so fast, caught some airtrain thing to another terminal, had staff waiting for us at security at that terminal and we were taken straight through, ran and jumped on the Orlando flight which was already fully boarded, they were waiting for us

Thank you Delta.
Anyway so we arrived in Orlando (a full day late). Our luggage didn't arrive on the flight because of the delay of the LAX flight, the bags didn't make the flight, so we lodged a lost bag claim with Delta. We were absolutely exhausted, it was now 48 hours since we left Australia, I hadn't slept in this time because I was calling from LAX to AKL to say we would be a day late but I completely forgot about magical express. So we headed to Magical Express (no luggage and not booking), gave them our luggage stubs and they said they will take care of it, find the bags and deliver them to our room and off we went to hop onto the Magical Express.
So you can still get the Magical Express. We were not booked with them for that day, but we did have a hotel reservation and it was fine, they didn't even question anything, I just gave them our hotel reservation number and they were more concerned with helping us to relax and make us at ease that they will find our bags. The bags arrived at the resort early evening.
So sorry for that long drawn out story

But Magical Express will not be a problem if you arrived a day after your ressie was booked. Actually, even if you changed your check in date, I would just keep my magical express booking as it is. They have to be booked seperately anyway and don't have to match your hotel booking.