My daughter just re-did a new floor routine this weekend, even though most of her gym keeps their routines for two years. Her old routine was fine. She was actually state floor champion last year with that routine, and it was easily up-gradable to her new level. But she fell in love with new music.
In talking to her coach/choreographer, she said the girls always do better with a routine they love. So, she is always willing to re-choreograph new music, or switch up routines. After all, the gymnast is the one who has to sell it, and it is much easier to perform when you love the music and the routine.
You need to talk to your main coach. It doesn't have to be a hard conversation. Just let her know that you fell in love with a new piece of music and you have already approached Coach X to choreograph it for you. Difficult conversations are much easier when you approach them directly and respectfully.