Is the switch bad or is it just because of a broken key?
I have taken a paper clip and strightend it out and made a very slight bend at the end and fished several keys out of switches.
As for changing it out... I just got a '91 and the plastic around the switch will come off, it just clips in. The plastic cowl under the steering column will come off with screws.
I had to remove an old security system from mine so I've seen the switch.
Hope this helps some.