You have a couple options depending on where the break happened.
If it happened close to the end of the line, you can simply re-equalize the lines you have. This would be taking the shortest line and then cutting
each of the other three to match the length of that one. You would not have to pre-stretch your lines as your lines have already been stretched to
their max by you flying on them for the period of time that you have. With good quality lines, nearly all of the creep (stretch) happens during the
first few flights of really stout wind. The stretch is the tightening of the braid. That being said, all you would have to do is to cut down and
re-sleeve your lines so they are all the same length.
To do this, stake the lines out on the ground at one end. Make sure that the lines are firmly staked and will not pull out. Go to the other end and
stretch all four lines out firmly as tight as you can get them. I use a screw driver and wrap the lines around it snugly so they don't slide off and
pull tight so they all stretch out equally. Once stretched out, use a sharpie or good marker and draw a line about 1.5 feet from the end of the
shortest line across all four lines. This marks all the lines equal length. Then cut four new pieces of sleeving material that are all equal length,
appx. 1 ft long. Sleeve all four lines, sliding the sleeving material up to the mark made above. Start with the first line, tie a keeper knot at the
end of the sleeving to hold it in place. Then fold the sleeving over to form the loop, lining both ends of the sleeving up so they are equal. Then
tie two knots, one at the end and one just under it go hold the loop. Do the same with the other three lines. Once done, slide a screw driver
through the four loops, pull against your stake and they should all pull equally. Trim off the lose ends as needed, fuse with a lighter to prevent
fraying.
Sleeving material - 10 bucks
Sleeving tool - 8 bucks.
Lines just as good as new, just a tiny bit shorter.
To make a new lineset, do the same but first tie loops in your ends and then stake them down, then repeat the above.
Bulk line can be purchased at most shops including ours.
Another hack, sleeve and loop the broken line and then add a long leader to that line to equalize it to the other three.
Hope this helps. If you need or have any other questions about making lines, let me know.
Happy Winds!
-Kent