To change your tune is to suddenly say the opposite of what you said before. You will change your tune soon enough.
It accuses somebody of inconsistency, usually once their own interest has shifted. The point is the timing rather than the change itself.
1phrasechange your tuneTo suddenly say the opposite of what you said before.
“You will change your tune when the bill arrives.”
change your tune is a phrase.
Practised in Idioms