Speaking of uniformity, Right Whale, your post seems better than most as the point to inject these questions for consideration:
1)If the speed of light has indeed changed has it changed uniformly over time, or has it changed in leaps or jumps?
2)If the speed of light has changed, were the changes universally instantaneous, i.e., did all photons in the Universe change their velocity at the same instant?
2a) If the answer to 2) is instantaneous, then >something< travels faster than the speed of light to deliver the message to all of the photons: "alright guys, lets jump it up (down) a notch or two."
We must at least have uniformity of definitions. The most powerful method of formulating definitions follows Bridgman. This might be a good time to review Bridgman procedures.