Data is good and can be very useful. Manipulated data is bad and can hurt you. What’s the point of collecting information in the first place if you’re going to mess with it? Your method of collection isn’t as accurate as you would like? You must stand behind the data you collected so far and move forward with another method instead. By adjusting numbers you’ve collected, you are misrepresenting the method or formula. Ethically better, I think, to publicly acknowledge a broken metric than stand behind massaged lies.
If the numbers are not for you and instead for someone else (boss, investor, customers, etc.), get to the bottom of why you want to change the numbers. If you feel the data misrepresents your business or project and worry that the numbers might throw you under the bus, it’s important to push back against the people asking for them in the first place. Again, better to admit a broken method than stand behind numbers that aren’t true. Honestly, I can think of no situation where it is ethically or practically appropriate to manipulate data you collected. It’s fine to do that in a budget or estimates, but actual cold hard data should not be toyed with. No one can learn anything from our lies except for the person with something to hide (or of course until the truth is revealed – don’t put yourself in that situation).
Be honest with yourself and your numbers. Don’t lie. Try a new formula instead.