Sheets tend to get “Exercised” though different position often enough so that they don’t get chafe points along their length, but Halyard spend a lot of their days winched down onto the same spots, so wear and stress appear at the same points every day for them.
Once a year or so, reverse you halyards, take them down, wash them and put them back up the opposite way so that those wear spots are moved along to a different part of the Halyard.
The easiest way is to stitch another line together with the Halyard and then pull them through. I prefer to wrap one layer of tape around the stitching as well and then some grease to help the join pass through the blocks and routers.
Be careful as you pull them through to ensure you do not destroy the join between the lines at an inopportune time, like halfway down the mast.