Can I do this in a story...?

You can't change names half way, it would confuse your readers. Unless your character has some name change or use as a codename etc. Try not to make it like it has always been their name since they're born. But you can use one of them as a middle name, I personally like the sound of Amara Raine -lastnamehere-. I choose Luke for a boy's name. Good luck!