I understand the sentiment.
You feel like it’s your body, your skull, so it should be your choice what happens to it after death. That’s a very natural and human feeling — wanting control over your remains and leaving something deeply personal to your loved ones.
However, the law doesn’t see it that way.
Your wishes in a will would likely be ignored or blocked by the funeral director, medical examiner, or court. Someone carrying out those instructions could face felony charges for mutilation of a corpse.