What if I change my mind about which primary school to send my child to?

Much as the gemeente in The Hague can help me with applying for a public school (Basis School) for my daughter, no one seems to know the answer to this question: What do I do if I have already put my child's name down for one school, but I'd actually like to select another one? Given that we are only allowed to apply for one school, this seems a pretty important thing to know. Can anyone help me with this? We have until early September to change our minds, but we are already signed up to one school's registration system... [To be honest, I find the registration system here in The Hague pretty illogical and unfair - there is a primary school just across the road from us, yet folks driving from Delft (all the children in one family, which may be as many as four or five children, given the size of many families here) may get a place there whilst my daughter does not...?! Not a very environmentally aware, or equitable system, in my humble opinion.]