And it is not always cosmetic either

Which is why I specified cosmetic surgery.

The word plastic in this case does not mean that actual plastic was inserted or injected.

And that is new to me! That makes more sense, plastic surgery being named after plasticity since it’s changing the shape of something and having it stay like that. Plasticity is the converse of elasticity (the latter describing a material that goes back to its original shape when deformed). I have added an edit to the post now.