I wouldn't necessarily say its a sin but well let me say it like this. God created you, every single inch of your body from your feet all the way to your hair, he chose the colour of your eyes, where your birthmarks are even how tall you are/ going to be. God is all powerful, all knowing, all loving. Now why would you want to change the way God made you. The Bible says to forget about outward appearance and focus on “that of your inner self, the unfading beauty of a gentle and quiet spirit, which is of great worth in God’s sight”.
I would also examine my heart and look at my motive around why I want this surgery, Jesus said to not be in the world but out of it, so dont care of things of this world, what people think or say, how the beauty standards are etc etc. I am also insecure about many things in my body, some are things that I can't change but I, well by time realised that I need not to focus on these things but on other things like my anger, or fear, things that matter and will affect my walk with God.
I want to leave you with this, getting a nosejob is not a sin but remeber that our society puts way too much emphasis on the body and not enough on the inside. God doesn’t do that. Remember what God told Samuel in 1 Samuel 16:7…
Don’t judge by a man’s face or height… I don’t make decisions the way you do! Men judge by outward appearance but I look at a man’s thoughts and intentions. Focus on God, he has a plan for you, he wants to work within you and develop within you.
Its funny how I give advice about God and religion when I myslef sin so much, at least i'm trying haha, anyway good luck boss on your journey.