If one is going to go to the trouble of laundering lines, that's the only way to do it.Of course it would be easier to use a runner to take the halyard off the boat and put it in a commercial washing machine but that wasn't the question.
I once thought it was correct and cool and technical to splice shackles onto my halyards, and that's what I did 20 years ago, even learning how to splice parallel core, low stretch stuff. Now, I put a Flemish eye on each end and tie one end to a shackle with a halyard hitch, seized. That way, I can end-for-end the halyard, thus extending its life, and easily swap it for a messenger for whatever reason.Attach a "messenger" line to the halyard and remove the entire line, if possible. If not, because you have shackles on both ends, for instance, then you can use the messenger line on both ends to wash 1/2 at a time. A bucket with dish soap, seems to be the popular method.
Google "reeving splice." The most reliable method.I tested cleaning a section of line and was very underwhelmed with the results so plan to remove the halyards for proper cleaning. The first two I tried did not work so good. I was careful with my butt-splice to not increase the diameter and keep it tight but the splice would not pass through the masthead sheeve. My halyards are all 3/8" diameter and that is the largest size recommended for the sheeves in the system and my splices will not fit through no matter how smoot I make them.
I am thinking that I will try to seize the line about 6" from the end and then pull back the cover to that point and taper the core over a couple of inches and then seize the cover at the end. That should reduce the diameter of the end of the line down to about half size and make it more supple.
Thanks for the suggestion thinwater. Will that loop without the core be smaller diameter and more supply than the rope with core?Google "reeving splice." The most reliable method.
I have not knot or hard spot other than the whipping which actually reduces the diameter. It is the square end of the halyard were the core and cover are whipped with the reeving loop.If you think in terms of a tapered splice instead of a butt splice and use a smaller leader such as paracord for your pull line you should be able to test it by pulling it across a square edge before even sending it back up the mast. I've often found that pulling a line with a hard spot or a knot in it will always hang up if there's a place for it to do that.