This 401(k) with Safe Harbor feature has decided to make a discretionary PS contribution - the first one since Plan inception ten years ago. The owner prefers not to receive any of it - can he simply waive his right? If so, would the waiver be permanent or can it be a year by year thing? Thanks in advance...

I'd say the first thing to do is read the plan document. Do you find any provision in there that would allow an employee to waive receiving the profit sharing contribution?

there is something called a one-time irrevicable waiver, but according to your comments the plan has existed for 10 years, so it is a little late for that.
if plan has a last day provision, then you could amend the plan to exclude the individual from the discretionary profit sharing, but that is about the only way I know how to handle it. if there is no hours requirement or last day provision, then the person in question has already accrued the money.
If there was a way to do it, I would be more than happy to accept the money, but I don't think you can do that either.

The IRS has approved, in some volume submitter documents, such a "waiver" - or whatever term is used to define it - by the HC employees. Apparently, they let it go through in some prototype documents during the GUST restatement, but I have not personally seen a newer prototype where it is allowed, whereas I have personally seen it in VS documents. I'd stick with Planman's advice and check your document - it should be pretty clear as to whether permissible or not.