Earlier quoted context omitted.
The article specifically mentions that he can and has since he turned 18: > When he turned 18, Thomas was encouraged to donate blood for himself. There is now no frozen blood bank in Switzerland, so his blood is stored in the rare blood banks in Paris and Amsterdam. And that his approval is required for doctors to draw into his "personal stash": > Since his blood can be given to anyone with a negative Rh blood type,…
> If he donates a unit for himself, he has to permit it to be used by anyone else who might need it. That sentence could have been worded better. This is the way I read it: If he donates a unit for himself, he must allow it to be used by anyone else who might need it.
I think your rewording still leaves that ambiguity, somewhat (though it does seem better), because i keep reading that as:
> he must allow it to be used..
Perhaps it would have been best to right it to break it down into two sentences.
He can donate blood for himself.
If someone needs it, they have to ask for his permission.
or He can donate blood for himself,
but then this makes it accessible to whoever is in need of it.