I don't know the true answer to your question, but here's a picture of the back of the module that includes our speedometer on our '06 Dynasty. It appears that it may be singly removable as a unit, albeit a bit tight and difficult to get at. Once apart, I can't imagine that you couldn't separate its shell, and hopefully get to where you find a bulb, or an LED.
It looks like it may be "squeezed" into the hole in the panel by a very large, 14 sided white plastic "nut". I do know that the plugs disconnect fairly easily, and if you can turn off that nut, it may come out the front, into our hands.
Do post whatever success you have. I'm sure it will happen to others, as well.