In my experience, if you back-sweeten, and the mead hasn't been chilled to remove the majority of the active yeast, fermentation will continue. I have faced this issue in the past, and each time I chill my fermentation vessel for a day or two before I bottle. This way the addition of some sugars will sweeten the mead rather than ferment away.
What happened to my comment? As I attempted to mentioned earlier, LMGTFY Top result says how to properly backsweeten mead.
What happened to my comment? As I attempted to mentioned earlier, LMGTFY Top result says how to properly backsweeten mead.