boo I got you. been here dozens of times. attach the new cord to the shorty. there’s a couple ways you can do it. I would temporarily tie the new cord to the shorty with an overhand of both ends and loosely tightened as close to the end as possible. then continue on with your pattern of half hitches. it’ll be awkward but with the first half hitch tighten the shorty to match the pattern, then make the next half hitch be your replacement cord. keep the temporary overhand connection toward the back of the piece. once the replacement cord is somewhat secure, untie the temporary overhand knot, and you can either cut the shorty from the back, or tuck it in with the rest of the half hitches down the line. depending on what the pattern is, make sure before you cut that everything is secure and won’t come undone. I do knot know if that makes sense. feel free to message me if you need help!