Writing a toy ad blocker is actually on my todo list :)

There's just so many things you can so. The original goal of the post was to tamper with zoom's attention tracking for example (which was a field in one of their protobuf payloads).

Proxomitron had that capability years ago - MITM proxy to filter pages and block ads, among other things. I still use it, it's very useful and continues to run fine on the newest Windows.