Didn't Google beat Hyrum's law by using their weight to force middleboxes to accept some variation in some datum of an http header or something?
Edit: hint: something about rotating a value for some number of decades. Either forcing the hand of middleboxes or CAs, I can't remember. In either case, it seemed like a real pain in the ass to keep the API observability concrete from hardening. :)
The other example of evading Hyrum's Law that comes to mind was when early Javascript users of JSON observed how they could intersperse comments.
Crocker said he noticed people were using the comments to stuff preprocessing directives into JSON.
He then devised the most ingenious hack: He told people they weren't allowed to put comments in JSON. Then people stopped putting comments in JSON.
I'm starting to wonder whether Hyrum's Law is really more of a suggestion. :)