You could re-sleeve the line, but you would have to re-adjust the other three lines to match your new line.
This process can be used to shorten a existing set of flying lines, equalise a set of lines that came with stitched ends, or repairing a set of lines. The start of the process is to stake out one end of the lines and cut the other end of lines to the same length, removing the old sleeved section.
1/ Start with the shortest line and slide one length of sleeveing onto the "fid" (very thin wire loop - Piano wire or Guitar string)
2a/ The looped end of the fid should appear from the end of the sleeveing. There are two options, I prefer this way
2b/ However some people prefer going through the side, so the hardened end does not wear the line.
3/ Insert the line through the loop of the Fid so the minimim pokes through.
4/ Push the sleeveing onto the line. It helps to "fluff up" the end of the line, and rotate the sleeveing while pushing
5/ Once the sleeving is on the line, pull the fid out of the end of the sleeving so a few cm of line protrude from the sleeving
6/ Tie a simple overhand knot near the end of the sleeving. Pull the knot tight
7/ Hold the knot then "walk" the sleeving up the line, using a milking action. Its important the sleeving is tight
8/ Repeat for the second (third and forth) lines. Pulling the lines tight ensure the end of the sleeve on the next line is level with the first. This is the easiest way to equal lines and relies on equal sleeves.
9/ Double the taut sleeve back double, so the ends of the sleeving are together. Form a flat loop for the double sleeve
10/ Tie a simple overhand knot, take care to ensure there are no twists in the knot
11/ One line tied, repeat for all other lines. Because the untied ends of the sleeving were equal, assuming you tie accurately the lines will be equal length.
12/ Use a flame to seal the tails of the lines
13/ Job done, a tidy knot that wont let you down.
