Measure 2 1/2 cups warm water in liquid measuring glass (water should be very hot but not boiling). In a small bowl, combine hot liquid and 2 packages of active dry yeast. Allow it to activate and foam up.
After yeast has activated, pour into bowl fit with a mixer. Combine cake mix, salt, vanilla and bread flour into mixer bowl with yeast. Use dough hook attachment to knead dough together, just for a minute or two.
Spray a large bowl with cooking spray and place dough inside. Cover with saran wrap or kitchen towel. Let sit for an hour until it doubles in size. Punch dough down with fists then cover again and allow it rise for an additional hour until it doubles in size again.
Prep a clean work surface and flour work surface. Once dough has gone through its second rise, remove and placed on clean floured surface. Using a rolling pin, roll dough out flat into a large rectangle shape.
Smear softened butter over top and evenly spread brown sugar over on top of butter. Spread yellow cake mix evenly over top of brown sugar. Rub gently to evenly cover if needed. Sprinkle with desired about of cinnamon and sprinkles.
On one of the long sides, roll up to make a long and skinny log. Slice into even rolls. It should yield 24-29 rolls depending on how thick you slice them.
Prepare a 9x13 baking pan or a large round baking pan with pan cooking spray/grease. About 12 rolls will fit in each.
Cover with plastic wrap and let cinnamon rolls rise a final time in the pan, about 30 minutes, or until they have doubled in size.
Bake at 350 degrees F for 15-20 minutes. Meanwhile, prepare frosting.
In a large bowl fit with stand mixer, beat butter, powdered sugar, cake mix, milk and vanilla extract. Add more powdered sugar/milk until desired consistency is reached. Add in as many sprinkles as desired.
Spread frosting over warm rolls. Sprinkle with additional sprinkles if desired. Cover with saran wrap to keep fresh.