MCDzienny

Is there a way to add cases to HandleMessage and HandleLogin in custom commands?

What exactly do you mean by add cases, or what are you trying to do?

I'm trying to add in CPE extensions that MCDzienny has yet to support and for that I need to add some case XX:'s to the HandleMessage byte and then I need to modify the HandleLogin void to allow the extensions to load to the player.

All the currently available CPE extensions are supported by MCDzienny. There are some extensions that are expected to be added to the client - for example hack control. When they do, the proper API will be added.

You can add your own CPE support methods without handling login or messages.