Rewrite HTTP response when error code received

Since you can't access HTTP::uri in the response, you'll need to set a variable in HTTP_REQUEST so you can access it.

If you look at the HTTP::retry command (see the last example on that page), you may be able to retry the request and change the request so you can get a different response from another server. (You may have to add some logic in your HTTP_REQUEST event to handle whatever host/location you use in the updated request).

If you ever wanted to just return a custom payload from within your iRule, you could use something like this codeshare entry to get you started.

Hope this helps