I have an S2 9.1 which is not the same vessel but built at the same time in the same shed. I seriously doubt that you have an encapsulated keel. Even if you did it would not be an issue. I assume you are getting lifted by two slings like everyone else so you need to get one sling in front of the keel and the other behind but positioned so you do not hit the shaft and strut.
Replacing the main halyard is not difficult. You likely have a rope to wire halyard if it is original, and you will likely go to an all rope halyard. You will have to attached a light line to the tail of your existing halyard and pull the old halyard down to the fore deck until it is replaced by the light line.
Then you attached the tail of the new halyard to the light line at the fore deck and pull the new halyard up to the top of the mast then down the mast and out the exit point. You really should go up the mast if it is not down and check that the sheave that the halyard runs through has not been chewed up by the wire. That will damage your nice new halyard.