I don't imagine you should have many problems doing what you are suggesting, which is the actual answer to your question.
I will also say that I think the passes are very expensive (we just spent $1300 for our upcoming April trip!-including one for a three year old), BUT, you might really consider how you'll feel about lying every day. We had a similiar situation on a trip to DL-my dd turned 3 in late Sept. and we went in mid Dec. Of course, the amount of money was significantly less! But, we just couldn't do it.
As an aside, my yongest son used to say he was three whenever someone asked his age (he was two at the time) I brought his birth certificate during that trip to DL, because I was sure someone would ask his age, and we'd look like we were lying, even though we weren't. However, we didn't need it at all.
Anyway, I didn't mean to go on and on-just really think about your decision carefully.
First trip: July, 1983
Second trip: April 17-20, Dixie Landings
April 20-28: Orange Lake COuntry Club