Game Management Guidelines (GMG's) aren't the laws but a set of clarifications around issues or interpretation that may have appeared in the period since the laws were last revised. They don't override the law set but provide colour to the grey mush that the book can be. In that respect they are similar to the High Tackle framework - referee's are expected to follow this framework but the law book only says:
9.13 - A player must not tackle an opponent early, late or dangerously. Dangerous tackling includes, but is not limited to, tackling or attempting to tackle an opponent above the line of the shoulders even if the tackle starts below the line of the shoulders.
Where does this talk about changing height of ball carrier/tackler, shoulder contact, etc?