Re: New guy with dumb questions.
1. How old is and "old boat"? Are you referring to wood hulls? Unless you are an independently wealthy romantic, or a shipwright don't even think about a wooden hull. But you mentioned a Cat 27, so I am assuming you meant a fiberglass hull. From what I know, or have read on the internet which is the same thing, hull rot is not really a problem with a full fiberglass hull. If the hull is cored, meaning has a wood core, then there could be problems. Decks are usually balsa cored and if there are leaks, then that is trouble.
2. The halyards and sheaves (pulleys) hold some pretty high tensions in certain conditions and can usually support a person. But, again, what BLJ said. It depends on your weight, the condition of your halyard, the size of the boat, the experience of the person helping you. If you don't have to do it, don't. I haven't had to do it in the 8 months I have owned my boat. Hopefully by the time you do you will have enough experience to understand whether it is safe on YOUR boat with YOUR crew and helpers. Not a dumb question at all, but an odd first question about sailboating.