A few days ago I posted this photo with the comment that I wasn't happy with the spacing of the colcolastic yarn and that I was going to resley the warp.
So last night I started re-sleying. To remove the header I just cut the weft and pulled it out rather than unweave it.
When nothing much is changing, just squeezing the yarns together in the same reed, I don't pull all the threads out. Instead I just move each bout of threads over one at a time. I find this makes it much easier and keeps the threads under tension and controlled until their turn comes. I loosen the knot of the next group and then just stick the hook into the next empty space grabbing the threads from the next dent to be moved. It only takes a few minutes and it's done.
I expect I'll weave this sample warp off today - IF I'm happy with the new spacing - and go through the workshop warps to see how many need to be updated. I've got a supply of 10/2 mercerized cotton now so that will probably be added as it is a yarn commonly used by US weavers.
As regards the colcolastic yarn, it is more fragile than I expected which is a bit disappointing, but now I know that I will take more care handling it as warp. I will suggest back to front beaming and lashing on rather than tieing knots as I did originally. These things are good to know so that people understand how to handle the yarn.