Hi Paul!
You’d never nuke your site — as long as you save a copy of the file you are editing first, right? 🙂 Always have a way to hit UNDO! 🙂
That code does work correctly, I’ve used it on many sites! If you have any problems with it let me know, there’s only one “gotcha” and that is if your theme is overriding the woocommerce_related_products_args filter which is an easy fix anyhow.
Cheers
Ben