As with most things, it is situational. I have no problem telling the defense the QB is taking a knee if the QB or Coach tell me he is taking a knee so I can protect the player. And, if the QB runs a play, I will flag an UNC. But, there is a big difference with the original question of a team saying they will spike the ball and then run a play. As long as you do not involve the official in your play call, there is nothing unfair about it. So, to the original question -- this is not a foul. They did not use any equipment or anything else in an unfair manner. Faked spiked ball is not different than a good play fake. Defense needs to watch the ball.
There is NO rule support for calling UNC for a QB lying to you. Telling the defense to stop playing isn't "preventive officiating", it's coaching, or worse, dictating the outcome. If a QB tells you he is taking a knee, why not just end the game? That's what you are doing anyway.
If the QB tells you he is taking a knee, remind him it's still a live ball until he does. If you feel you have to tell the defense something (and you really don't), you say, "Let's play smart IF they take a knee."
Team A is up by 4 with 50 seconds to play. They are on their own 5 yard line, B has no time outs. QB tells you he is taking a knee, you tell the defense, "He's taking a knee, lay off." QB fumbles the snap. You have just told the defense to lay off, effectively keeping them from recovering the fumble which could change the outcome of the game.
Let the game come to you, call the game you see, and quit coaching! There isn't another play in football where you would tell the offense or defense how to play. Why do it here?