I've had two 16 sails that were cut down to fit a 14 and they worked, but I just wasn't happy with them. First, you cut pretty much the whole bottom section off of the 16 sail, which basically takes all the shape out of the sail. It makes the sail completely flat. If you just do that, the sail won't fit on a 14 boom, so you need the 16 boom and then it sticks out a few inches in the back. You would want to cut a little bit of the foot off to make it fit a 14 boom. If you use the 16 boom, you would have to move the block hangers because they are way too far back.
I wouldn't cut it down. You would ruin a perfectly good 16 sail that you could sell and you would have almost no resail value to the altered sail.