No, but you can install the ir package and turn it off remotely.
You could search for a programme about going to sleep (bound to be something appropriate on CBeebies!), record it and then set up a macro in ir to play it?!?
A message is possible: you would have to create a web page somewhere convenient and then use the target Humax's TV Portal to display it. Alternatively, create a .jpg or a .mpg containing the message and make the target Humax play it through the media browser, but the sequence of button presses required would be trickier than the TV Portal idea.
Re the TV Portal, you can use Telnet access to point the home page anywhere you like. All you then need to do to display the "message" is force a "TV Portal" button press through the WebIF virtual remote, followed by "Exit" to return to the live programme.