Blimey OP, dramatic much?!
Your blind ignorance of the topic is the problem here. There is an abundance of information about organ donation that you can access in seconds. I’m not sure why you think it’s hard work.
If this is something that really worries you, you need to get clued up. Dying is an important life event you know and there are 100s of decisions to make.
Here’s just some things I’ve picked out from your posts:
You need to get a firm grip on the difference between donating your body to medical science and donating your organs. In neither case the government own your body, even in an opt out situation (look up definition of ‘donation’).
You will always have the final say over what’s donated, as you do now. When you put yourself on the register (but would take yourself off if it changed to opt out
) you will have ticked what you are willing to donate if those organs are healthy enough. As far as I know, heads and faces aren’t on the list 
There are stringent rules around tissue donations and sampling. When I say stringent, I mean strict as fuck. It’s a massive deal for pathology departments and hospitals everywhere. See The Human Tissue Act 2004.
Please stop being hysterical now and get informed. Once you have enough correct information then make the decision that is the right one for you and you alone.