It is possible, but getting them torqued back down to the right spec is hard. If you dont care about the right torque spec. Then take the old ones off ( make sure you don't loose the keys, there is one on each cam) and then put the new on and tighten the bolt down the best you can. Then retime it and put the timing belt on. When you tighten the timing belt back to the right tension. Then go back to the bolts holding cam gears on and get a wrench and tighten it to were you cant. Once you get to this point put the wrench back on the bolt to were you can hit it with a hammer or a small 5lb. sledge(best universal tool). Dont wack it just give it a good tap so it tightens it up good. While your doing this make sure it doesn't jump a tooth or anything. There you go