Then why can't you go marry two or three women in the temple? The doctrine now is not that a living man can be sealed to many living women.
You've answered your own question as to how. A living man may be sealed to more than one woman. Plural marriage is still a doctrine and it hasn't changed. Only the practice of it.
And the Church has not repudiated not allowing descendents of Cain to have the priesthood for a time.But its not a doctrine.
Sure it is. The doctrine always was that they would have the priesthood at some point and now they have. Abraham 1, not being expunged from the scriptures, shows that this doctrine is still valid.
Sure, there has been no official repudiation of the former position, but the position doesn't hold any longer.
The promised as merely been fulfilled. Where is the change in doctrine?
Exactly - so they're lying -
I don't believe they are. But those who do not understand the doctrine, especially those who are hoping for a change and because the Church has indeed presented a different face, are going to think so and that is a good sub issue here. I believe there are a whole host of people who are rejoicing that teh Church is changing it's doctrine when in fact it's not.
they do know the reason, which doctrinally, is because blacks are supposed to be descended from Cain, who was cursed for murdering Abel.
A reason given, but the doctrine actually resides in Abraham 1 which denies the priesthood to the descendents of Ham.
Does/has revelation ever changed doctrine?
Yes. And revelation has been claimed in the face of public opinion. But has revelation in that case actually changed any doctrines? No, I can't think of any.