If something is "cast in stone" or "carved in stone" it means it is rigid and inflexible or even authoritative. This expression is most commonly used in the negative to say that something is still open to change.
ex. His ideas about marriage are not cast in stone.
ex. She acted like all of her opinions were carved in stone.
If you "put the finishing touches" on something, it means you do the last things you have to do before you are done.
ex. I'm almost done with this painting. I just need to put the finishing touches on it.
ex. She delayed her husband for another twenty minutes while she put the finishing touches on her makeup.