If you don't want to make new scales you can either put stuff on the existing scales, or take stuff off. Putting stuff on a flat knife scale that gets pulled in and out of a pocket doesn't always stay in place for long, although if you don't like skateboard tape you could epoxy on some real sharkskin, maybe a stronger adhesive would help it stay put. To add texture by material removal you could file in some cross-hatched lines, or draw a grid and then use a ball-tip Dremel bit to make dimples in each box. Or you could carefully mark evenly-spaced lines along just the outer edges of the scales and then use a round file to relieve each mark.