Funny premise - I don't know that any song has changed my life.
But I do remember a moment, I was sitting in my living room, DH (then bf) was there, some of his friends, our mutual friends were there. I was about 2 years out from an emotionally abusive headfuck relationship, on my own with DS1 who would have been about 2 or 3 at the time. I had been going through a really strange period where it was like during the relationship, I'd blocked out every emotion and forgotten how to relate to people (because my ex had forbidden me from having any friends except his friends) so it was almost like I was learning to have emotions again. I used to walk to Blockbusters and rent a different 3 films every week and watch them and just cry or laugh or whatever it was.
Anyway I was sitting at this party, NYE I think, and the Foo Fighters came on:
It's times like these you learn to live again
It's times like these you give and give again
It's times like these you learn to love again
It's times like these time and time again
And then when my cousin died in 2020, one of the songs that came up and made me think of her was Kate Rusby's Hunter Moon. It caught me originally because of the lyrics:
The end of the day will come soon
And the stars in my lonely sky,
Are infinite bright,
And the stars know my soul will fly,
They're holding it tight.
But towards the end of the song there's the lyric:
For she's the sun, I'm only the moon.
It made me think that my cousin was such a brilliant, vibrant person, she was so loved and everyone was so shocked and upset when she died. But she was also the kind of person who surrounded herself by other brilliant people. Basically everyone that I ever met who loved her was brilliant as well, it made me think about the nature of the moon reflecting back the sun's light, and whether my cousin was the light that sent brilliance back to all those people, or whether she was a moon that was reflecting everyone else. It made me resolve to try to be both as well. To be a light to inspire others, but also to try and be more like anyone that I admire and reflect their light back into the world. If my lovely cousin can't be here any more then at least there are all these people in the world who she did touch and she did light up when she was here.
Anyway it turns out the song is actually meant to be about the moon being in love with the sun 
but I prefer my meaning.