Outside (again)
A little but important update to my post on Lightroom's Auto Sync feature. Ctrl/Cmd clicking the Sync button switches you “permanently” into that mode, but there's more - holding down Alt/Opt + Ctrl/Cmd changes the button's display and switches you temporarily into Auto Sync mode. So hold down Alt/Opt + Ctrl/Cmd and use the mouse to drag a slider - Lightroom applies the adjustment to all selected images.