You do not have to change string/cables on that bow once you change cams. That cam is also draw length specific. You can get small amounts of adjustability out of it by twisting the cable (twists in to lengthen, twists out to shorten) but only maybe 3/8" or so. Mathews makes cams in 1/2" lengths for draw length. Your best bet is to call your local Mathews shop and have them fix you up with the correct cam and then retime the bow for you.