We'll use alphabet beads which have a 3.5mm size bead hole, as a reference:
Crimp covers, which are larger than the bead hole size, pinch into place right over the cording, and can work well with the 2mm cord you're using. You can add glue to the inside of the crimp cover to secure them so they don't move around. GS Hypo Fabric Cement is labeled for leather; you can review the glue information chart to locate other options.
Another option is to use crimp tubes. This finding will fit over cording of this size and keep the alphabet beads in place. Slide them onto the cording, compress the center section with a pair of chain-nose pliers and they will stay put, keeping your message right in line. They are not much smaller than most alphabet beads and measure 6x4mm (inside diameter of 2.5mm). If you use a different size cording, choose the crimp tube with the appropriate inside diameter measurement--they are suitable for cords ranging from 1-4mm.
You can also experiment with finding a bead with a hole size that will fit over the cord, is larger than the alphabet bead's hole size and is also similar in size or smaller than the alphabet beads so it doesn't interfere with your design. Glue the beads to the cording to keep your message in place.