When adding a single bead addon to a critter, string one end of the cord through a row of beads like normal. When stringing the other end, exit the row at the point that you would like to add a bead, string on one additional bead, and reenter the row at the next bead to complete the row.
The previous technique can also be used as an anchor for larger addons. Exit the base row at the point which you would like an addon, begin a fringe or ladder stitch at that point, and reenter the row ar the next bead. If adding on a ladder stitch, you will need to snake the cord back down to the base of the addon through the already-added beads.