add a second autoconvert button, "full convert". this one places priority on upgraded cards over keeping a playset of unupgraded. having both buttons lets people swap between the two configurations at will.
another way to name them is to add "autoconvert" as a header over two buttons "upped" and "unupped"
also if we wanna get really fancy, add a third button for "unupped shiny" for people who really want to show off their bling in league