It's not possible to do that and use the fast JavaScript engine from WKWebView. I'm sorry but you have no idea what you're talking about.
What's the technical issue?
Thats only used for user initiated navigation, not loading of assets.
You could still inject a JavaScript file or CSS file though to help hide pieces of the view. But that would be content blocking after the HTTP requests have been made.
I don’t know of a way to intercept the HTTP requests as they’re being made from a WKWebView like Safari does for content blocking.