The phrase "change tune" refers to changing one's opinion or approach on a particular matter. Some antonyms for this phrase include sticking to one's guns, maintaining one's position, being steadfast, or standing firm. These expressions suggest a resolute commitment to one's beliefs, rather than flip-flopping or wavering. Another antonym might be "digging in one's heels," which means to become even more stubborn or inflexible in one's stance. While changing one's tune can sometimes demonstrate adaptability and openness to new ideas, these antonyms emphasize the importance of conviction and unwavering conviction in one's beliefs or actions.