Can an executor overturn a designation of beneficiary per the decedent's will?

A will must be presented to probate court for allowance. By that process the court determines that the will is valid. The only person who can change a bequest is a judge. That rarely happens and only for a very good reason. The executor of the estate must follow the provisions in the will to the letter. If for some reason the provisions cannot be carried out the executor must ask the judge for guidance.