So, if I read this correctly, there's no way to modify the results of a request anymore? I can just redirect to a new URL, block or allow? I' m not even sure, upon reading that, if I can use JS to redirect based on the full URL not just the matching snippet to a new URL.

I wrote that previous comment before I fully understood the new specification. I'm still not entirely sure, but it looks like you're right.

I thought the rules were static, I see now they can be updated dynamically — which works perfectly for my use case.