Yes, but how does any of that affect the decision of "Yes, it's OK for Al to make this comedy song"? He's not asking her to put her name on it or positively review it — just to say she doesn't mind him doing it. So I don't see how "subtle variations" make any difference. As he said, this was the first time he'd encountered this in many decades of making parodies, so if you're implying that this is just how musicians work, you're wrong.