Is there a way to enable this option again in the loader?
Shift-Click does
not remove the thing you click on. Instead, it sets the selector for that slot to "None". If the selector already says "None", then clicking will be ineffective.
If you're
loading SWF files manually (via the "Swf Mod..." button), then Shift-Click won't achieve anything.
If you've
registered your SWF files via the
moreClothing mod, and then activated them at runtime via the selectors (or by loading a particular charCode) then a Shift-Click
will remove that piece of clothing.
If you're loading SWF files
via character folders then it's hit-or-miss. If the SWF file is a vanilla import, then the basic clothing and accessories (TOP, BOTTOMS, EARRING, etc) will tend to vanish when Shift-Clicked. BODY mods are less reliable (and long sleeves are frequently implemented as a BODY mod, so they can be tricky to remove). If the SWF file is a Loader mod then it will usually ignore your clicks entirely
(although a few - such as Mike's - will flip through different appearances when clicked).