I think the directions you read mean that you're not supposed to put hot liquid in the shaker jar along with a packet and shake ... I've done this and the top will fly off and you'll have you next Medifast meal splattered all over the kitchen ... it literally BLOWS up!!!.
I'm certainly no expert but I personally LOVE to take the Hot Chocolate and put it in my blender with cold coffee and some coffee ice cubes and blend away, it makes a Frapuccino type drink ... YUMMY!!! Does it ruin the meal? I don't think so but maybe Nutrisystem could confirm that..
I started on Medifast in late June and I've iced almost all of my cappuccinos, chais and hot chocolates. As a matter of fact, last night I blended the hot chocolate with 1 tablespoon of PB2, 1-1/2 tablespoons of Davinci SF caramel syrup, and ice and had a wonderful iced beverage that tasted a LOT like a Snicker's bar As the weather turns cool, I'm sure I'll start heating these beverages, but they are wonderful iced!..
Don't worry about it I love them both iced, and the nutrition is the same either way!..
I too have had both the 'hot' chocolate and the cappucino cold, it's just too hot in Cal. in the summer to make very much hot food, so I improvised. Tasted fine and I believe I read before trying this that it's perfectly acceptable to do..
The "DO NOT PREPARE IN SHAKER JAR" instructions definitely apply to using HOT water...steam needs a place to go...and it's up~hence the top popping off. My ABSOLUTE FAVORITE hot drink is the hot chocolate with a LOT of ice cubes (5-6) with a dash of cinnamon, a teaspoon of SF white chocolate syrup and about 6 ounces of water...30 seconds in the Magic Bullet (I just got the Medifast blender for my birthday too) and it's like eating Oprah's favorite Frozen Hot Chocolate!..