How does Lea Salonga sing a whole soprano song with her chest voice?
First of all that’s a mezzo song, not a soprano song. Second of all she’s not singing with her chest voice for all of it (only the lower parts/ low middle parts) she just has a voice of a darker timbre, a heavier weight, and/or tessitura. I don’t think you can change the timbre of your voice but you can practice sing loud by breathing with your diaphragm, and it your voice may change as you age. She’s not a soprano though her voice is heavier than one, she might be an alto or mezzo.