There is only one instance that I might consider trying to change the color of a crown that has been cemented into place, and that is IF 1) the color of the crown is DARKER than the adjacent teeth, and 2) if the ceramist put a surface layer of color onto the crown. If both of those two conditions are met, the dentist might "try" to remove the darker surface layer of porcelain with polishing diamonds and polishers, leaving a slightly lighter final color.
If that doesn't work, or wasn't possible because the two conditions weren't met, then replacing the crown with a better matching color crown would be the best way to go.
However, saying all of that, today using highly polishable modern dental porcelain for crowns rarely results in the crown changing color over time. More often than not, it is the other adjacent natural teeth that discolor over time. One exception might be when a semi-translucent ALL-porcelain crown (i.e. no metal underneath) is used and the underlying tooth discolors over time, yielding a darker looking tooth. This happens occasionally when a tooth undergoes trauma (called traumatic discoloration) and/or ends up needing a root canal treatment.