Ok, first, schools do not diagnose. They determine a child eligible or ineligible for special education, under one of the 13 eligibility categories.
In my 15 years of doing this, I have seen many kids incorrectly categorized as ED instead of autism, because when autistic needs are not met, the child often displays behaviors similar to ED.
However, what gives me reason to pause is that your neuropsych said aspberger which is no longer in the DSM and hasn't been for over 10 years. Nevertheless the child in front of you should match the child on paper.
What you're asking the school to do is to change eligibility category based on the neuropsych eval instead of the school's eval. Be careful, because if the neuropsych report also says anxiety, that certainly qualifies for ED.
If this is what you want, you need to make a formal request to make this change, and you'll receive their decision on a NOREP. And no, another set of evals is not necessary (by law) to do this. Ask them to show you where it says that, if that is their sticking point. A school can choose to use an outside eval if they want.