I've ended up with six pounds of packaged sliced apples. Ingredients read: Green apples, Calcium Ascorbate (Calcium, Ascorbic Aci(Vitamin C)) added to maintain color.

I know preservatives are generally a no-no, and can kill yeast or drive it dormant. Can I use it in a fermentation if I cook the apples first?

I'm trying the apple butter cyser (applebuttercyser.com) and figured I'd make my own apple butter for it. Will boiling these down make them safe for use in primary?

shouldn't have any problem from the ascorbic. I wouldn't cook them or you may set pectins and make a hazy cyser.

In fact don't yeast like vit. C? I don't see any real preservatives in your apples. You could soften then puree them in hot water and add to the cyser.