The halyard actually stays outside the mast, as it runs through a pulley at the top of the rotating stay, and in effect rotates with the stay, so fortunately it's not a case of having to re-run it through the mast.
Good tip about sewing whipping cord through the two ends - smart I'll be doing that from now on...
I've also been to a chandlers and had a look at some rigging screws/ turnbuckles etc, I now see how the counterpoised threads mean that turning the bit in the middle further apart (slackens the shroud) and turning the other way brings the threaded sections closer (tightens the shroud), more confident I can do this now!
I think the anchor point for the forestay has a spare hole on which I can use to rig up the mainsheet as a pulley.
