I would advise you to take a look at XNormal.

This program calculates a normal map from two 3d models. You take one model, put it into Blender (for example), make it high-poly and sculpt the hell out of it. You load both the original and the sculptes model into XNormal (AFAIK they don't need to have the same geometry) and you will get the differences as a normal map.

If you apply this normal map to your (original) model, it will look very much like the sculpted one.

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

Avatar image of me done by Chidori.