For: Lightroom 4+

Here are a couple of handy shortcuts for altering an image’s develop settings from the Library Module (as well as the Develop Module).

Shortcut	Keystroke (Win)	Keystroke (Mac)
Reset Image	Ctrl + Shift + R	Cmd + Shift + R
Convert to Black and White	V	V
Match Tonal Exposures	Ctrl + Alt + Shift + M	Cmd + Option + Shift + M
Copy Develop Settings	Ctrl + Shift + C	Cmd + Shift + C
Paste Develop Settings	Ctrl + Shift + V	Cmd + Shift + V
Sync Settings	Ctrl + Shift + S	Cmd + Shift + S