Pasteurizing means it was heated to kill bacteria. You are more than welcome to add the two different juices together , or pitch the yeast separately and see which juice makes a better cider.
I don't understand your question about racking before pitching. Racking from one carboy to another, a fermentor to a secondary, a primary to a bottling bucket is usually done to move the beer off the trub so as not to reintroduce off flavors into the product, and to allow for bottling, aging, or clearing of beer.
I'm also not sure if the sulfite is a yeast nutrient at this point, or a product for stopping the fermentation when the final gravity you want is achieved.
Help us out?