INSERT INTO mytable
SELECT col1, col2, <newValueCol3>, col4, col5, ...
  FROM mytable
  WHERE Col3 = <ValueCol3>, ColN = <ValueColN>

>I need to select a set of rows from a table, based on two columns
>, give one of those columns a new value in the selected set, and then insert the selected set into the source table.
>I can bring them down from the server, do the changes and then insert them one at a time, but I'm not crazy about that all those trips to and from the server, I'd rather do it all on the server, but can't figure out how
>