With my ciders/grafs, after fermentation is complete and everything has settled (sometimes I cold crash, sometimes not) I bottle with frozen apple juice concentrate. Usually 1 can per 5G batch, but I might use 2 cans if I want it a little sweet. I bottle one in a plastic soda bottle, squeeze out the air and cap. When that bottle is turgid, I know the rest are also carbonated. I chill the soda bottle and taste it. If it's where I want it, then I cooler pasteurize the rest of the batch to stop fermentation. Result= carbonated, cidery goodness at the sweetness level I'm looking for (I usually like them dry). The thread on cooler pasteurization is also on this area of the forum, so there's another thing you can search for.
I have also used Xylitol to backsweeten fruit beers. Have used 1 cup per 2G batch of Grapefruit or Cranberry Moon (American Wheat). I usually don't backsweeten the raspberry, apricot or blueberry versions.