AHH, thanks for the claification re: hard and still. Did those bottles in the fridge retain some sweetness? I assume you throw them in after a week or so, yes? will they still age, or does that shut them down where they are?
Freeze thaw? How does that work? Do I freeze apple juice, let it thaw and collect just the juice from the thaw?
That is rather my aim. Half of them to be slightly sweeter but carbbed, the rest dry.
Just like with pasteurizing, you need a test bottle to know when carbonation is at the right spot. Throw them in the fridge and it stops fermenting (depending on yeast) and leaves whatever sweetness is left. I've only done this with an 8-pack at a time (yield from a gallon) and for no more than a month. Long term is not recommended.
Note that this only works if you let the ferment finish completely and cleared, then back sweetened. If you try to cold stop the ferment while it's still active you'll get bottle bombs even in the fridge. There's just too much yeast in there.
Freeze/thaw yes as you said. Home made concentrate.