Have you ever threaded a warp, started to weave and then discovered that you have made a threading error? in the middle of the warp? Do you undo what you have woven so far, and rethread your loom (muttering a few unspeakable utterances as you do so?)
An alternative to rethreading, especially if the error is near the middle of a +700 end warp is to use replacement heddles, tied to the correct shaft. In this particular example, I have incorrectly threaded a pattern sequence, repeating it once too many times – in the middle, of course.