You can put whatever text you like in there that the
calibre template language supports. For your screenshot don't forget to put a # in front of any custom column names, so #status not status.
You mention series a couple of times - you don't need to use the custom text feature to display series, it is already displayed (as ticked in your screenshot - just that your book selected does not have the series populated). If you mean to show a secondary series column, then yes that is certainly possible like any other custom column.