Ten years ago I added four extra treadles to my Spring when I upgraded from 8 to 12 shafts. I remember just following the instructions and having no trouble at all. What I do recommend, though, is something I learned from the world of knitting patterns -- that is to read ALL of the instructions before starting, and highlighting anything that says "at the same time". Be sure you are confident about the order of operations before you begin. But you shouldn't have any issues, I remember adding the extra shafts and heddles took me maybe three hours, and you're not adding the extra shafts. Best of luck!