It's really easy. The bulb with it's holder is available at the dealer, usually for less than $5.00 It is hard to find otherwise. You must transfer over the green sleeve or the clock will no longer light up in green. If you have to replace the green sleeve, they were available at partsexpress.com. You can find the part numbers for both the bulb and the green sleeve if you search through the old forums.
To change the light, first you must remove the clock. It is just pried out of it's position in the dash surround trim. Early Mystiques are harder because the dash surround must be removed for access. Once it is out of the dash a few inches, disconnect the wiring connector. On the back side you can find the bulb with it's intregra holder. It's usually black. It has kind of a cross cut in it so it can be twisted with a small screwdriver. Reverse the directions to install the new one.