I cold crash, rack to keg, add a little concentrate, purge keg, shake, and taste. I add ~1/4 can at a time tasting along the way. You can always add more if you need more sweetness, but the other way around isn't as easy. I like my ciders semi-dry and usually end up adding ~1 can of concentrate for a 5 gal keg. To get the sweetness of a woodchuck or hornsbys I'm guessing you'd need closer to ~2 cans of concentrate.