The "howToPublish" parameter of NetStream.publish command does not work.
But you can do it client-side by changing the StreamType from the client like this:
"append" does have meaning however. If you do not use the "append" flag, subsequent publish commands with the same stream name will cause earlier versions to be versioned:
netconnection.call("setStreamType",null, "record"); // or "live-record"
// then create new NetStream object with the NetConnection object
var netstream:NetStream = new NetStream(netconnection);
myStream.flv will be the most recent.
myStream_0.flv will be the previous recording.
If you do it like this myStream.flv will be appended instead: