Is it illegal to nym-shift?
No. Not illegal.
Is shifting nyms four or five times a day proper? Particularly, among adults? I say no. Usenet does have some standards and protocols that reasonable people follow.
Shifting nyms causes problems trying to filter the unwashed. Why have to filter each nym-shift, multiple times a day.
Filtering the entire domain is what I could try, but if I do that I might not learn something from a responsible and decent poster that actually has something to contribute to a subject.