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If it's not really about tuning or wiring. Then it belongs in here.
Is diesel Knock harmful to the engine?
Do you mean at idle and light running, or when "tuning"?
The former, no - assuming it is actually the fuelling and not an actual mechanical issue, the latter is usually as a result of over-advanced injector timing, and is like over-advanced ignition, which is a bad thing.
Just following up on Gords great reply, this webinar is worth a watch for more information and some demonstration on the dyno: https://www.hpacademy.com/previous-webinars/161-understanding-pilot-pulse-diesel-tuning/
This also touches on it in passing: https://www.hpacademy.com/previous-webinars/159-diesel-tuning-fundamentals/