Is it possible to change server secret code by RCON?

[Regeneration]

I'm hosting a few servers and I can't figure out if there's a command to secure a server with password or not (toggle between public and private server). I tried the command list but there is nothing there.

If there isn't, where can I find a guide for the custom command feature?

[Pieface]

Unfortunately you can only do this by changing it in the configurator and then restarting your servers.

You can find information about writing custom server commands here. You'll need to first define them in JSON format and then monitor your server logs for when they get called so you can apply custom code. Won't allow you to change the password of the server remotely though.