I see it all too often – a beneficiary confirms that the deceased had changed their mind about leaving money to a particular charity, or even a person, and wants to know if anything can be done after the fact. The short answer is, emphatically, no. Once you die, your will is set in stone, barring a court order – which is not easy to obtain, and having forgotten to update your will is never a valid reason.
If you change your mind, you absolutely must write it down, Don’t make changes on a copy of your will; don’t make unwitnessed changes on a typed will. See your lawyer, do it right, and then you won’t need to worry about what will happen later.