Can I tag a file from Quick Look?
The Tags feature in Finder1 already has a keyboard shortcut which can be activated whilst in Quick Look. Press ⌘⇧T to set a tag on the currently selected file.



To set a custom shortcut…


Open System Preferences → Keyboard → Shortcuts → App Shortcuts.
Click the + button to add a new shortcut.
Set the Application to Finder.app, and the Menu Title to Tags….
Set your keyboard shortcut and press Add.


1 As this is a feature of Finder, not Quick Look, the modal popup may be behind the Quick Look window.