It may not be hard to actually remove and replace the cam gears, but remember to get them off you need to remove the timing belt which is rarely an easy task. Then you have to make sure all your timing marks line up before you put the belt back on or else you'll screw your engine up bad.

And like many people have said, it wouldnt be worth puting only cam gears on. After market cams are mainly for lightening purposes and shaving one pound or so, it isnt going to do anything