The temperature controller for the Chevy SSR is a sealed unit, but the lamps that are used for night time illumination are replaceable.
You do not need to take the sealed unit apart to get to them. If you look at the back of the unit. There you will see 3 areas that are indented with what looks like 3 white screws. Those screws are the lamp holders. They are very tall and need soldering. If you replace one I would suggest replacing all 3 to keep the lighting level even on the control unit.
Below is an image of back of the unit and it shows the white lamp connector in the upper left of picture, unscrew with a common blade screwdriver.
Below is a picture of the lamp installed on the board from the inside. Please note the height. When I install new lamps I solder longer leads so that the lights sit in the OEM sockets. They are a neo style lamp but I have not found a plug and play variant so I reuse the OEM socket and simply replace the old lamp with a new one or led upgrade and add length to the leg connections to keep them the same distance to the dial face.
If you are interested in my assistance to replace the lamp with incandescent or an LED upgrade please send me a message and I will provide cost and shipping information.