I can't remember where I read this, or if it's true (sorry, not a great source, I know), but I believe they include preservatives (sorbate and sulfite) which kill yeast and prevent spoilage, which makes sense since the pack is full of sugar.
I would recommend adding the sweetening pack to taste when you degas and add stabilizing additives. You would have to stir it often to taste test, but it would just degas the wine more.
MOD EDIT: Sig only takes up 6 lines now. Fermenting: Apple cider x 2, Doppelbock, Red, Oatmeal Stout, West Coast IPA x 2
Bottle conditioning: RIS
Keg conditioning: La Fin du Monde clone
On tap: Maudite clone, Double Munchen, Oktoberfeast, Oktoberfest Pilsner
Planning: Brewed in 2011: 22 (2010: 15, 2009: 29, 2008: 21, 2007: 1)
Wine made in 2010: 6 kits (2009: 19, 2008: 30)