Can Exiting Crowns Be Sculpted, then Polished?

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.

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!