Thanks for this - been wanting it for ever.
One suggestion, a tweak to exclude a set of columns. If empty copy and paste all, of course. I would want to exclude pubdate.
Fortunately I wasn't using Ctrl+C or Ctrl+V for anything, so I made them Edit metadata->Cut and Paste - wonderful.
If anybody's wondering, Paste works on multiple books.
Best Enhancement since . . .
let's say '-' and '=' to clear and set dates to now, and ' ' to clear ints and floats (I regard those as a boxed set)
BR