quote: How can I mark this membership in the members list?
Is this an Admin-only task or not ? Basically you have to alter the form/s and the SQL to alter the value. In the short term (maybe always) just use something like TableEditor to get to the database
quote: How can I add a column to the table or an icon to the left column?
Same as above, alter the SQL and then the ASP code to display the value in the desired location.