You adjust car engines hot when idling because they use hydraulic tappets that are pumped up with oil pressure to get them to work correctly.   Most of these sorts of systems are "adjusted" at the center of the rocker pivot and all you are doing is removing all system clatter.

The Savage has pure mechanical tappets, adjusted stone cold at top dead center using an adjuster screw at the outermost moving tip of the rocker arm -- you'd have to be the Flash operating at full hyper speed to do it while it was running.