For all intents and purposes they cannot be done in the car. You could change them, but you'd have to pull the transmission to get the rear one out and replace the cam plug, and you've have to drop the crank to verify the correct placement. Plus you'd have no way to clearance them as Chryco said. You need to pul it and pull the crank (pistons can stay in the bores - just tie the rods out of the way...
Cam bearings are clearance by shaving with a bearing knife or utility knife blade. They should not be honed or shaped with any type of abrasive because the abrasive will embed in the bearing surface and tear things up when it's running.
