Your ordinary juice apples are not the same type of apples used to make cider, generally. Cider apples have a lot more tannin, and are generally inedible. The tannins in cider apples help give the cider depth, which would be lacking in regular apple juice. I have had luck in the past brewing up very strong tea to add to store bought juice, but it’s still not the same.

Hmmm, I suppose you could try adding some apple juice concentrate, but of course fermentation would start up again and you'd end with a higher alcohol content. Even then, dry ciders from store bought juice tend to be pretty thin on flavor. General solution is to add tannins, acid blend, and/or backsweeten.

I've tried adding tea and hops recently and really enjoyed both!

I use malic acid to tune acidity, earl grey tea to play with tannins, and you can always cut up a few pounds of apples and throw them in there to get some of the flavors from the skins + flesh.