How can we change the shade of the crown which is permanently cemented, without removing it?

The crown has to be removed and rubricated. Try doing a custom shade at the lab, may get you closer.

The only way to really change the shade of the crown is to have it redone. If you saw and approved the shade before it was cemented, you may need to pay for a new one unless the dentist is OK with redoing it for free. If you did not approve of the shade first, then the dentist should definitely redo it for you.

Your best bet is to Redo the Dental crown and use a dental laboratory that does custom work.However, If for some unknown reason, you must keep the crown and do not want to remove it,You can also prepare the crown, as a veneer preparation, at this time, take an impression and order a customized porcelain veneer, with the exact color desired and bond it to the prepared crown!Ordepending on the contour of the existing crown, order a no prep veneer, or lumineer.Or After the preparation, Bond composite to match, depending on your skill level.In certain selective cases, such as long span bridges, I had done above procedure and had great success!Treat the porcelain as the porcelain repair! Best of luck to you.