Might I suggest replacing the knots with split rings? It will make for a flatter and more comfortable joint, and make o-ring replacement faster.

You should be able to get very small (6-9mm) split rings at any craft or fishing tackle store. Run about 1-2 inches of cord through the ring, fold it back on itself to make a 1/2 turn, and serve or whip the cord to itself to form an eye through the split ring. Use the paracord internal strands for whipping and use generic tacky glue or Beacon Fabri-tac on the whipping to make sure it won't unravel.