Assuming the Constitution isn't replaced with something that better fits pro-White values, not much. Aside from removing illegals and other non-citizens, most of what a White-nationalist would be able to accomplish would be broad strokes directives, such as requiring federal voter ID encouraging disenfranchisement for criminals, providing school vouchers for families within certain income bracket, etc.

What I would like to see is some exile-based sentence for criminals where a condition for freedom is renunciation of citizenship. Ideally it would be arranged with another country (in Africa most likely), but even if it could possibly be done, it would be a logistical mess.