non replacable instrment cluster bulb??

im pulling my instrument gauge cluster to replace it with one that i got out of a "u pull it" salvage yard and while im at it i want to replace the gauge bulbs to blue or red or something else maybe, beside the speedo cable hook up on the cluster there is black thing screwed to the cluster, looks like a bulb in there but no way to get it out, its all made together, can anyone shed any light on what purpose this little thing has or does. truck is 88 s10 blazer 4wd 4.3L.