The verb alter has 5 senses (first 3 from tagged texts)
1. (26) change, alter, modify -- (cause to change; make different; cause a transformation; "The advent of the automobile may have altered the growth pattern of the city"; "The discussion has changed my thinking about the issue")
2. (2) change, alter, vary -- (make or become different in some particular way, without permanently losing one's or its former characteristics or essence; "her mood changes in accordance with the weather"; "The supermarket's selection of vegetables varies according to the season")
3. (1) alter -- (make an alteration to; "This dress needs to be altered")
4. interpolate, alter, falsify -- (insert words into texts, often falsifying it thereby)
5. alter, neuter, spay, castrate -- (remove the ovaries of; "Is your cat spayed?")