Optimizing redirects to avoid TCL error "Multiple redirect/respond invocations"

If those other rules contain redirect or respond commands, that'll be the issue. You're best bet is to combine any of the rules that contain redirect/respond commands. I'd also carefully check your rule logic to ensure a request can't match two criterea by using elseif and/or return statements. Here's an example (a bit overkill) using your rule above;

when HTTP_REQUEST {
 log local0. "Found [HTTP::host]"
 if { [HTTP::path] equals "/" or [HTTP::path] equals "/vod" } {
  HTTP::path "/vod/"
 }
 set rdr_target [class match -value [HTTP::uri] equals some_uri_redirects]
 if { $rdr_target ne "" } {
  HTTP::respond 301 Location $rdr_target
  log local0. "Found match with value = $rdr_target"
  return
  }
 elseif { [HTTP::path] starts_with "/watch" } {
  HTTP::respond 301 Location "http://blabla/vod/page/default/home.do"
  return
  }
 elseif { [HTTP::host] equals "blabla" } {
  log local0. "Found [HTTP::host]"
  set rdr_target [class match -value [HTTP::uri] equals someother_uri_redirects]
   if { $rdr_target ne "" } {
    HTTP::respond 301 Location $rdr_target
    log local0. "Found match with value = $rdr_target for blabla"
    return
    } 
   else {
    if { [TCP::local_port] equals "80" } {
    HTTP::respond 301 Location "http://blabla[HTTP::uri]"
    return
    } else { 
      HTTP::redirect "https://blabla[HTTP::uri]"
    }
  }
  }
}