I don't believe for a minute that Cessna designed, or allowed to enter into service, an aircraft whose horizontal stabilizer 'switches' from providing downforce at the tail to lift at the tail at any point during flight. Why? Because for that to happen, it would either result from or require a MASSIVE change in the CG. The downforce required is the same at liftoff, climb, cruise, and approach speed- remember that the fuselage acts as a see-saw suspended from the Center of Lift. Downforce is not a function of airspeed, it's a function of masses and the Center of Lift. If you have to REMOVE downforce from the tail end, it means you've REMOVED the load at the other end. You can't just say that it switches without thinking about why you had the downforce in the first place. If there's evidence from a deposition, can you post a link to the information, or at least a reference to the particular case where the engineer made this claim?

Look, a Caravan is built like a big 172 or 182. Neither of those a/c allow the CG to get aft of the Center of Lift. NO Cessna, Piper, Beech, Cirrus, etc., is designed that way. If any a/c were designed to 'switch' in the manner suggested, it would be so sensitive to pitch force changes that it would be virtually uncontrollable.

Now, as for the different procedure for the de-ice fluid? I'm willing to bet that rather than trying to blow the fluid off the plane, the revised procedures take into account the fact that a high-viscosity fluid coating the surface can disrupt airflow as it ripples and flows, and the revised procedures are designed to modify speeds/angles of attack to counteract the change in surface characteristics caused by the presence of the heavier fluids.