I’ve had a negative outcome in the past adding a person (grandparent) later. Our first night after check in we were stopped at Epcot for over 2 hours trying to validate that we had legitimate tickets (traveling from the Midwest, DD stood dehydrating in fleece pants, had planned on quickly entering and buying a dress, didn’t notice she hadn’t changed until we were in the bus, had stopped in our room to change before heading out). We were told it was because we visited too many times and had several MBs on our account (can’t be true because we are not annual passholders and had been to WDW around 7-8 times with 3-4 MBs on one account - party of 6). We lost the 2.5 hrs of regular park time and our FPs (unusable). CM was unapologetic and said we had extra magic hours. We had proof of payment and
MDE showed tickets and we made sure our bands were working at the front desk at our resort (AKL) before heading to the park. The front desk assured us all bands were active. The stress alone put a huge damper and the grandparent felt awful. We barely had time to grab something to eat as park was closing.
We assumed everything was fixed at Epcot (we entered Hs and AK just fine) and the CM assured us it was, but when we tried to get bands for
MNSSHP (2-3 nights later) for said grandparent the same issue came up and a CM with an iPad took 1.5 hr and we lost 2 FPs before the party (4.30-6 pm). CM was again unapologetic, reinstated FPs which were now unusable and said you have the party to ride rides.
We had taken grandparents before successfully but this was the first time adding just one grandparent to an existing package. I believe it was because we had some sort of discount (Disney Visa or dining can’t remember which) and had added a person later which flagged us.
It’s an easy call to have a person removed from a discounted package and a minimal charge if it’s close to check in day.