Something altered has been changed. You might have squeezed into an altered version of your high school cheerleading costume for your 20th reunion — hoping your classmates would exclaim, "You haven't been altered at all!"
Altered is an adjective to describe anything that has been changed or altered. You might need altered clothing after you succeed at your diet, or you might feel like you are in an "altered state" after you've been hypnotized. Altered behavior is behavior you have changed, like the altered behavior of your housebroken dog.
