Can neutrophilic rhinosinusitis be preventable?

Probably. The diagnosis that you have provided suggests that you have had a biopsy. Neutrophiles are the first line of defense in what is called innate immunity and usually indicates an infectious origin. Therefore, it is preventable if it is a viral or bacterial infection. If the diagnosis was made by an ENT specialist, he should be able to give you an appropriate answer. Avoid people who are ill.