I have done exactly what you want to do. I have booked a 3-night stay at ASMu for DS and I to celebrate his 5th birthday this month using a PIN I got last October - saved 30% on that room.
At the same time, I booked a room for the whole family at BC with a 40% discount thanks to the PIN.
Fast forward to a week or so ago. A dear friend, who did not know we were going this summer, emails to ask if we would consider going with their family as she thinks her DH would change his mind about WDW if they went with "an expert." Apparently, their last trip involved inlaws, people not making ADRs, people not leaving the resort until noon, not having a plan, and having to eat a lot of chicken tenders and burgers because they didn't know where else to eat. I started twitching just thinking about it, LOL.
So, I call CRO, get a less than helpful CM who tells me that while I can change my resort and reservation dates, I can't book a room for friends using the PIN (he kept saying things like you can't put 8 people in a cabin - I KNOW, that is why I wanted a second cabin, sir). However, he put me through to the grand gathering line, and we were able to add another cabin using the PIN.
So all told, I have a January reservation for one room, and a June reservation for two cabins.
Have a great trip!