Hi Mike,
It sounded like you wanted to change the 200 status to a 400. But your test rule is trying to rewrite a redirect (which would be a 30x status) to a 404. Can you use a browser plugin like HttpFox for Firefox or Fiddler for IE to determine exactly what the application is sending back and then describe what you want to do with it?
Unfortunately, HTTP::status can only be used to get (not set) the status of the response. So to "change" the status you could need to send your own response using HTTP::respond. It's fairly simple if you can send your own response content. Or if you need to leave the response data from the server in tact, you'd need to collect the payload for the specific responses and then use HTTP::respond to send a 404 response with the original payload. You can check the HTTP::collect wiki page (
Click here) for examples.
Aaron