Don't bother disconnecting the battery. You'll then need to code the radio, etc. You could pop the fuses for the instrument panel.
Your car has no speedo cable.
Your cluster has no "wires" to be disconnected. It's molex plugs that pop out when you pull the cluster.
Buy the tools, pop the cluster, replace ALL the bulbs (why go back in soon?) and push it back in.
1998 C230 "Black Betty"