301 to Redirect

If it's static strings, the change is pretty simple. Just look in responses for a 30x status, then set the Location header to a value with the app's host replaced with the outside host name.

when HTTP_RESPONSE {
    Check for redirects
   if {[HTTP::is_redirect]}{
       Log a debug message.  Comment this out when done testing.
      log local0. "[IP::client_addr]:[TCP::client_port]: Updating Location header from [HTTP::header value Location], \
         to: [string map -nocase {find replace} [HTTP::header value Location]]"
       Replace the Location header with the new host name
      HTTP::header replace Location [string map -nocase {find replace} [HTTP::header value Location]]
   }
}

Replace 'find' with the string you want to search for and 'replace' with the string you want to replace it with.

Aaron