Golden blood is the rarest blood type you can have in the world. So rare they estimate that less 50 people have it worldwide. Its also known as Rh-null blood because unlike being Rh negative (such as O- or B-) they have no Rh antigens at all, like not a single one out of the 61 possible antigens at all. This is because of a mutation that essentially leads to the carbon backbone the antigens are formed on not existing on the red cells. This also makes it ideally the absolute best transfusion blood because it will not cause any reactions no matter what the receivers blood type is. However because so few people have it and it is so rare, any blood that is donated of it is saved in a small pool for other people with golden blood, as if they require a transfusion they cannot accept any other blood without risk of a transfusion reaction.

Don't forget people with the Golden blood type too! While Bombay is an exception to the ABO typing golden blood is an exception to the Rh typing

CAR T-cells don't work on the next generation they actually die out in the body so I don't know what you're on about there

Ive done a lot of work on CAR T-cells so in that regard technically yes you can alter the bodies immune system to attack cancer cells, but we do it by taking those white blood cells out the body, altering them and then putting them back, not by changing the bodies genetic makeup itself