You can; we actually plan on doing that since my current AP expires in May but our trip isn't until September (I'm not renewing because I need a later expiration date for next year's trip). The thing is, if you are booked on an AP rate, you will need to stop by Guest Services to upgrade your ticket first so you can present the new AP at the front desk. Disney Springs is usually the best option or failing that, Guest Services at the International Gateway.
You're welcome, I just hope you can find a discount elsewhere.