Attm. San Francisco sailors on sail size
Cutting down a sail is not a good idea for a couple of reasons. A sail is designed for a particular wind range. If you cut down a larger headsail that was designed for true wind speeds lets say up to 15 knots and you use it in winds of up to 25 knots, you will probably damage the sail material. Some laminates will never recover to their designed shape after being used in excessive wind speeds, even if it only happens once. Also, if you cut down a larger headsail to something smaller, the draft will not be in the correct location unless you remove material from both the luff and leech. This brings other problems as you should now alter the reinforcing patches on the tack, head and clew. Just keep what you have and look for another sail if you need something smaller and heavier.
What is the highest true wind speed your boat can comfortably handle with the 140% headsail? The design of your boat has a lot to do with its sail carrying ability. Some boats will be able to carry more area, under control, than others.