If you're trying to rewrite the response without the user seeing a redirect then the HTTP::uri command won't quite get you there, as it won't rewrite a response URI, just a request URI. What you'd need to do is use the HTTP::header command to rewrite the locaiton.
You can do this with the "HTTP::header replace" command. If you wanted to send a location of
www.bob.com you could do:
when HTTP_RESPONSE {
HTTP::header replace location "http://www.bob.com"
}
This is obviously a very basic example, but that's the command you're looking for, I think.
Colin