Are you talking about G2? b/c there was no speedo cable in G2 cluster guage ...Yah, you can replace speedometer. Follow the link above to remove the cowl, you'll want to disconnect the electrical connectors as well. The cluster is held in by 4 screws, then disconnect the electrical connections on that and the speedo cable. You have to take apart the cluster to switch the sspeedometer, but its not hard, I did it on mine because my speedometer was not working either and it was the problem.
A couple tips-
check all your bulbs while you got it apart
Make sure the plastic warning light covers are seated correctly when you put it back together
Grease your speedo cable to keep it from squeaking