Easiest way to route / replace cable is to lower board, disconnect cable and then spice new cable into old.... then slowly pull from the top until new is threw. Then reattach as needed.
Regarding the pin, while the board is hanging down use a thin piece of wood, maybe a yard stick and slide it up the trunk until you hit the pin. Then use that to match the outside of keel as a best estimate and begin to sand..... you will eventually find the pin location. But why do you need to remove it?
good luck