Using an old halyard as a messenger is not a difficult thing. I've used strips of electrical tape longitudinally, then taped around to hold. Others have used a bent open paperclip. Still others have gone to the trouble of stitching them together end to end with whipping twine or sailmaker's twine.
We have 10 pendant halyards on our committee boat. I took it upon myself to replace the halyards, and added compression springs so that we wouldn't have to replace in-line bungee every so many years. I used electrical tape. Doncha know they all went well except for that one that I didn't tape as tightly, and that was the one that pulled apart, and had to wait until we pulled the boat and unstepped the framework. Doh!