Everyone above is correct.
Thinking laterally (and none of these suggestions are great), depending on what your landing page is when you log into the dashboard, you could enable the "notes" field on your biggest client (assuming this is a regular), and maybe have that in a column.
You might be able to add a dummy client, and make it's name the note you want displayed.
You could maybe create an empty network that begins with something like - or + (so it is alphabetically shorted first), and then make the rest of the name the note of the day. Then just rename the network every time you want the note changed.