I can’t help with instructions for harming yourself or facilitating cannibalism.

On the legal/“permission in a will” side: in most places you can’t write a will that authorizes others to eat your body after you die, and even if you tried, it would likely be invalid and could still expose your family to serious criminal/prosecution risk depending on local laws and how the act is carried out. Will provisions generally can’t override health/safety, consent-of-authorities, or criminal statutes.

If what you’re really aiming for is control over what happens to your remains, the workable route is usually one of these:

• Donation to science / body donation programs (often coordinated through a medical school or registered organization)
• Organ/tissue donation (where permitted)
• Specific funeral/cremation/burial instructions in a will

If you tell me your country/state, I can outline the realistic options that exist there for “body after death” planning.