You can absolutely get an AP instead of a PAP when time to renew a current PAP comes. You will get the renewal rate on the AP.
The only time you cannot "trade down" is once you purchase a PAP, you cannot decide that you made a mistake or that you won't use the water parks, DQ, etc enough to make the extra cost worth it and want to drop down to an AP then. You can do it when the PAP runs out but not while it is still valid.