What is the ruling on cremating the dead after several years have passed since their burial?

Breaking the bones of a deceased person is like breaking them while they are alive, and burning after death is like burning while alive, and it is one of the greatest abominations and crimes. Scholars have explicitly forbidden sitting on graves or walking over them, so how much more so digging them up and burning the corpse? This is only permissible if they are the graves of polytheists and there is a need to exhume them, as the Prophet (peace and blessings be upon him) exhumed the graves of polytheists and built his mosque in their place.