Adding strands to a braid is easier, when you add two instead of one by one. It depends how you normally braid. I´ll try to explain it with the braiding “over” method (the other would be the braiding “under” method). Usually you take one of the outer strands , let´s say here the right one and cross it
over the center strand(s) (eventually followed by another step like in the 4 strand round braid, where you first cross over 2, then turn back crossing under 1). Then you repeat the step with the other outer strand, in this example the left one. O.k., until now, this is a normal braid.
Now you add the strands. Take a cord that is double in length like each strand you want to add. Take it at the center and bring it behind (=under) your braid, in a manner that the braid and the new cord cross rectangular. Now you continue braiding using the method described above but together with the right outer strand you take the right part of the new cord. Do the same with the left outer cord and the left part of the added cord. Make sure that you make a tight braid, otherwise there will be a small loop at the center of the added cord. That´s all.
Tapering is also easier, when you drop two strands (on opposite sides of the braid). Then you can fix them with a short west country whipping, i.e. tie them together with a simple knot on one side of the braid then with another knot on the opposite side. When you want to skip only one strand you can untwist it, if possible, and then do the same as I wrote for the two strands.
If you drop many strands on a short piece of braid, like it`s often done at the first part of the release cord, then simply cut the dropped strands so, that only a short piece remains. Then make a straight whipping over the whole tapering area. Note, that a too thick or too long whipping can cause problems with the ammo release. Therefore you could make also a reversed sling. You start braiding from the end of the release cord, near the pouch you add the strands, make the pouch and then drop the strands and make the whipping. A thick whipping or a stiff part on the pouch-near retention cord doesn`t cause problems.
Good luck and have fun with experimenting