How to add double line ruling to bottom of first row of table

[Callie Bertsche]

I inherited a scripting guide with many tables.
These tables all have one header row, with an associated paragraph tag,
and multiple paragraph tags used within the subsequent rows.
Some of these header rows have a double line ruling between the header
row and the rest of the table.
Some tables' header rows have only a single line ruling.
 
How do I add a double line ruling to the header rows that have only a
single line ruling?
I've tried using the Table Designer, looked on the Ruling page, and the
tables have "Double" selected for the Separators and Rows drop-down
menus in the Heading and Footing Ruling region of the page. No matter
what combination of Heading and Footing Rulings I try, it only affects
the last row in the table, not the header row. 
 
Thanks,
Callie