I was able to upgrade my Citipass to a five day pass when we visited in June. We then decided on the fifth day to upgrade again to Annual passes, with no problems.
I want to say about about $80 (guess paid cash) more for the 5 day pass, and another $80 (sure on this one) to upgrade to the annual passes. (Two passes one adult and one child's ticket.
Friendly advice since I have two of these for my upcoming trip:
Heaven forbid you ask this question to any DL telephone or email representative!! They will give you the runaround and then tell you they won't know till you show up with it. Simply don't waste your time. The best answer I got was in a thread I asked about a couple weeks ago, simply plan for the worst case scenario, basically paying the difference between a full cost 4/5 day hopper with a discounted 3 day park hopper.