Can Exiting Crowns Be Sculpted, then Polished?

I personally dont like to do that when possible because I like to have the original glaze on them,but in dentistry we have to do things in office sometimes to make the crown look and fit better...

You absolutely can improve on the shape of your crowns by contouring them.  There are some limitations.  Some crowns are made and then a thin layer of stain is applied to get the color desired.  Other times the color is integral to the ceramic.  If the crown has a thin layer of surface stain, and you remove it, the color may be changed in the area adjusted.  Most of the time, it won't take much to make a big difference in the appearance.  The big thing is to be sure you've got the right dentist doing this for you.  Best of luck to you in perfecting your smile!

As long as the thickness of the porcelain is adequate and you are happy with the color of the crowns a good cosmetic dentist can reshape and repolish a bulky veneer or crown to give and excellent result.  If the thickness of the porcelain is too thin because the preparation of the teeth was not adequate, sculpting may make the underlying prepared tooth visible and require that the teeth be prepared adequately and the crowns replaced so that they are not too bulky.  I would suggest that you return to the dentist who placed the crowns originally to have any reshaping done for this reason. 

However, depending on the material, there can be a limit to how much can be done.  If there is a metal substructure, aggressive contouring can expose the metal.  Also, the polish may not get as shiny and smooth as if they were left untouched.  It might get very close, but if may be difficult.