Is this possible? If so, is it difficult? We'll probably be purchasing 3 day single park tickets through AAA. I know we'll want to spend two days at IOA because WWoHP is our main reason for this trip. I'm unsure if we will want more time at US but don't want to completely give up the option. So, can we decide to add park to park so our third day can be both OR even add a fourth day to our single park passes?