There are lots of ways to do this. Abrading the faces with sandpaper or similar, the coarser the grit the coarser the resultant finish. You can also sculpt the G10 with files or a Dremel tool. Roughness can also be added by adding grit, such as grip tape, epoxy and walnut shell media, sand, etc.
Removal of material tends to look cleaner than addition of material.