You normally use one of the battery hold-down rods threaded into a handy boss near the timing belt tensioner pulley to hold the tensioner in a near-normal position while you remove the tensioner piston. That said, I wouldn't get too excited about the potential for damage, since whatever moved one or more of your cams would have been a very slight force (this assumes your mechanic wasn't doing something crazy, of course). No reason to think that kind of minor force would jam a valve into a piston with enough force to do anything dramatic.
What I like to do is to get the rear cam line up, slip on the belt, then wrap a zip tie through one of the pulley holes and around the belt (so it can't slip). Then around the front cam, another zip tie, then around the rest of the path, and one more zip tie around both portions of the belt above the crank pulley. Then after I install and release the tensioner piston (and check all the timing marks one more time), I cut off the zip ties. Works like a champ, and will keep you from accidentally bumping the belt out of position.
What I like to do is to get the rear cam line up, slip on the belt, then wrap a zip tie through one of the pulley holes and around the belt (so it can't slip). Then around the front cam, another zip tie, then around the rest of the path, and one more zip tie around both portions of the belt above the crank pulley. Then after I install and release the tensioner piston (and check all the timing marks one more time), I cut off the zip ties. Works like a champ, and will keep you from accidentally bumping the belt out of position.
