I booked a Minivan (MVAR) at Denver International Airport for later this year. However, I need 4WD/AWD, but they were sold out of those. If my minivan doesn't have 4WD/AWD and I see a vehicle with it in the PC lot, am I allowed to pick that vehicle instead?
Your MVAR will not have 4WD/AWD because none of them do. If you are a PC and have an MVAR reservatiion, then yes, you would be able to pull one from the PC section of Ultimate Choice for no additional charge. The chances of that actually happening though are slim since they tend to hold those back for upgrades when they are in demand. You can of course try to pay for an upgrade assuming one is available, but it probably will not be cheap.