What can I use to decorate leather cord that is already sealed on both ends?
Hang a pendant on it. The link to hold the pendant must be able to open and close securely. Choose metal that will *not* promote base metal allergies. Common safety pins rubbing against bare skin will give some people oozing welts. Alternatively, use the cord as a base for macramé and incorporate the desired beads in the macramé. Common materials include silk, linen and hemp. DMC’s glow-in-the-dark thread is fine for “wrapping”, but it’s synthetic and doesn’t knot easily or hold knots without glue or similar. Wrap 1″ sections of the cord with GP wire and hang eye-pin or similar drops laden with the desired beads between the sections. If the cords are chocker-length, you could pair them and suspend the beads between two cords, with wire-wrapped spacing as described in previous paragraph.