I am not sure how it would be possible to change your face into someone else's face. But for the purposes of this question, let's say you could, maybe by painting your face, using makeup, getting plastic surgery, wearing a mask, being one of the Faceless Men on Game of Thrones, or assuming their identity entirely. Depending on what you're specifically doing, you could say:
You should paint your face to look like Harvey's
You should do your makeup to look like Harvey's face
You should do your face like Harvey's
You should get work* done on your face to look like Harvey
You should wear a mask of Harvey's face
You should swap faces with Harvey
You should wear Harvey's face
You should morph into Harvey
You should shapeshift into Harvey
You should become Harvey
*where work is a common euphemism for "plastic surgery"
If your face is made out of some malleable material like clay or silicone, maybe like the type of makeup they use in the movies, your original thought is good. I don't know about "a Harvey"; I'd probably just say "Harvey" or "Harvey's (face)". mold and model are similar words to sculpt that you can also use.
I don't know of an idiomatic expression that sounds best, especially not in general for all of these possibilities. But maybe this could work:
You should model your face after Harvey's
where "model after X" just means something like "copy X".