A 'comments' type field (like the synopses shows in) accepts random strings .
Use the Custom columns tool to add columns.
Columns add to the bulk of the database, less is more performance retention. don't go wild adding columns.
I would avoid using a 'standard Calibre column" even if it would accept the paste. One get metadata click, could stomp on what you had there, with it being replaced by ther results.
If you were clipping From Calibre, you can paste into just about any APP that allows values of the type you clipped. (text, integer, floating)