im not thinking so. if it could be done, youd have to remove the rad, grille and maybe bumper to slide it out from behind the timing cover, after you have removed the harmonic balancer. then youll have to remove all the rocker arms, or at least loosen them so that all the pressure is off the cam. then rotate the cam to push all the lifters up in their bores, and slide the cam out. but you also need to replace the lifters cause they wont last long on cam number 2. and obviously dont forget to block off the fuel pump hole on the block cause you wont need it anymore, assuming youre putting a 4.0 cam into a 4.2
oh, and the lifters cant be removed through the head, you have to pull the head to get them out.