How can more preload change the way the engine runs? It can’t. It will only change if the lifter Is bottomed out. Oil viscosity has nothing to do with it. This issue is a case of the lifter bleeding down when stationary load is applied. If the lifter is functioning properly, this doesn’t happen. Obviously there are issues with some lifters. When the lifter fails to hold oil it bleeds and increases lash. The extra preload is a bandaid to keep the pushrod in the cup. Nothing more, nothing less. If it works in your situation it could be a good alternative to swapping parts.
Doug