Can I edit an existing table in CB Profit Poster?

Sure!

Just go to edit (or create) a post or page. You will see the CB Profit Poster widget below the content text area. Select the table you want to edit from the drop down menu, and click the "edit" button.

Your existing table will open up in a new tab and you will be able to make any changes you want to it, like modify entries, change their order or remove them altogether. Click the blue "save" button in the end.