Intercept status codes and redirect

Your condition is not easy to track. You can have multiple HTTP requests passing through the F5 in random order for multiple connections. Making a decision based on a sequence of HTTP status code in a single connection seems a bit complicated. I would recommend trying to make a decision based on a specific value in the HTTP request instead of tracking multiple status codes.

You should be able to do something like this for a simple redirect based on status code:

when HTTP_RESPONSE {
  if { [HTTP::status] == 404 } {
    HTTP::redirect "http://www.example.com/not_found.html"
 }
}