I don't understand how the endlinks can pre-load the sway bar. The only load it can take is one side higher or lower than the other, by torsional twisting. Now maybe the rubber sway bar bushings (holding the bar to the chassis) are loaded/binding up, both twisting same way to get to the new lower ride height. If the bar is not free to move to a lower position, I can see needing to release & re-tighten them esp if they are stock.
Not disputing what you're saying just not seeing it in my head what you mean when you say the bar was pre-loaded.