The phrase "changed one's ways" is an idiom used to describe someone who has made a significant improvement in their behavior or habits. Antonyms for this phrase could include "stagnated," "regressed," or "relapsed." These words suggest a lack of progress or even a backwards movement in someone's personal development. Other antonyms could include "stubborn," "resistant," or "unwilling," which describe a person who is resistant to change or unwilling to consider altering their behavior. Overall, the antonyms for "changed one's ways" suggest a lack of personal growth or development, and depict someone who is stagnant or unresponsive to the need for change.