Blues Brother, you will not find a written reference in any WT publication. As I related above, the CO visited each congregation and shared a "letter" from headquarters with the elders telling them that from then on anyone unrepentantly taking a blood transfusion will be considered as having disassociated themselves. The WTS did tell BBC News that (see my quote above). The elders were not allowed to touch, let alone read the "letter" and were not given a copy for their files. They were just instructed to write in in the margin of their elders manual. The CO even said that what he was reading was "not a letter."
There is nothing in print in the WTS publications regarding disassociation. BBC had a reference to it. When the CO visited each congregation, at the elders meeting, he verbally told them that it had changed to disassocation. He read it from a piece of paper with WT header but would not let the elders look at this "non-letter" nor was a copy given to the elders.
http://news.bbc.co.uk/2/hi/790967.stm (below is quote from this article)
But if this looks like a major climbdown, a spokesman for the organisation - also called Watch Tower - insisted it was merely a procedural change.
He said not taking blood remains a biblical injunction and a core tenet of the faith.
If a member has a transfusion, they will, by their actions disassociate themselves from the religion. The ruling emphasises personal choice, he said.
He added that if they repented afterwards, they would be offered spiritual comfort and the possibility of redemption.
But the distinction between what in other words amounts to resigning rather than being sacked, does seem to be a major shift.