You sure can! Use Brimlock, Nylon Hat Wire, or another wire that you prefer for hat brims. Leave two inches and then begin crocheting over the wire as you begin the final round of the hat. Once you have 2" left, cut the wire so the last 2" overlap with the first. Seal the two ends where they overlap with joiners or tape. Finish the last round. Alternately, you can add the wire after finishing the last round. Add it in the same way, only crochet over it after making the last patterned round by adding on a round of single crochet in each stitch. If you like, you can then make another round of single crochet OVER the previous round so that the wire is better hidden and the brim edge is thicker.