sing a different tune

sing a different tune

To change one's opinion, behavior, or attitude, especially suddenly or abruptly. He never used to support that political candidate, but he's singing a different tune all of a sudden. I used to be very cynical about the world, but ever since surviving that car wreck, I've been singing a different tune! They'll be singing a different tune after they see what we've come up with.
See also: different, sing, tune
Farlex Dictionary of Idioms.

sing a different tune

 and sing another tune
Fig. to change one's manner, usually from bad to good. (Almost the same as dance to another tune.) When she learned that I was a bank director, she began to sing a different tune. You will sing another tune as soon as you find out how right I am!
See also: different, sing, tune
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

sing a different tune

Also, sing another tune. See change one's tune.
See also: different, sing, tune
The American Heritage® Dictionary of Idioms by Christine Ammer.

sing a different tune

or

sing a different song

1. If someone sings a different tune or sings a different song, they express an opinion which is the opposite of the opinion that they expressed a short time ago. Only a week ago, Peters was insisting that the minister resign yet suddenly, for no apparent reason, he is singing a different tune. Note: You can also say that someone sings the same tune or sings the same song, meaning that they continue to express the same opinion. The president basically sent the signal that he's going to keep singing the same tune he's been singing.
2. If people sing a different tune or sing a different song, they express different opinions about the same subject. The problem of homelessness is very serious and it doesn't help that two Government departments are singing different songs. Note: You can also say that people sing the same tune or sing the same song, to mean that they express the same opinion about something. The party were at last united, all singing the same tune.
See also: different, sing, tune
Collins COBUILD Idioms Dictionary, 3rd ed.

sing a different tune (or song)

change your opinion about or attitude towards someone or something.
See also: different, sing, tune
Farlex Partner Idioms Dictionary

sing a different ˈsong/ˈtune

(be forced to) change your opinion: Anne says she wants a large family but I’m sure she’ll be singing a different tune when she’s had one or two children.
See also: different, sing, song, tune
Farlex Partner Idioms Dictionary
See also:
  • change one's tune, to
  • sing a different song
  • sing a different song/tune
  • sing another tune
  • backpedal
  • abortive action
  • be living on borrowed time
  • pull the rug from under
  • pull the rug from under someone/something
  • pull the rug out