How to forward requests to subfolders in pool?

If (as Colin mentions) you're terminating SSL at the BIG-IP, and you just need to forward to the server in cleartext but with a different URI, you could use something like:

when HTTP_REQUEST {
  if { [HTTP::uri] eq "/prod/ups" } {
      [HTTP::uri] "/receiver/ups"
      pool y.y.y.y
  }
}

If you need to replace the "/prod/ups" string and leave the rest of a longer URI intact, you can use string map:

when HTTP_REQUEST {
  if { [HTTP::uri] starts_with "/prod/ups" } {
      [HTTP::uri] [string map {/prod/ups /receiver/ups} [HTTP::uri]] 
      pool y.y.y.y
  }
}

/deb