I get a bit geeky when it comes to formulating fly fishing leaders, unfortunately only to hack them up when adding new droppers. This usually happens after a few fly changes on the dropper and left with a stub. instead of cutting your main leader, try this nifty way to add a new dropper.
Be it a blood knot, surgeons knot, or whatever, leaving the existing knot is key to the process. Tie the new dropper above the existing knot by using a Uni-knot then slide it down against the existing knot.
That’s it – you’re good to go!