Yes, I know what gnulib-tool does. It just doesn't seem legal to me. I don't buy the existence of an "inside group" with special knowledge as a rationale for making changes in basic legalisms. I hope Brett will comment.
always sign his paintings on the painting itself, rather than on a label next to it. No, it's different. As I wrote, you're explicitly changing/overriding a license statement. Not augmenting a file with an unstated license. As we all know, there are cases where it's not feasible to write a copyright statement in the file itself (images, etc.). That's not what's happening here. Unless your argument is that all these files are copyrighted by the FSF, and we're acting on behalf of the FSF, and therefore we can downlicenses from GPL to LGPL at will. But if we can, it seems to me anyone can (we're not FSF employees ...). It all seems like a very dangerous precedent. karl