My apalogies, DBF cannot be used there. You could use...

SELECT originaltable
COPY STRUCTURE TO temp
ALTER TABLE temp ADD COLUMN newfield c(20)
APPEND FROM originaltable

You could also scan through the original table if you would want to write data to the newly added fields on a record by record basis.

SELECT originaltable
SCAN
    INSERT INTO temp(field1, field2, field3, newfield) ;
       VALUES(originaltable.field1, originaltable.field2, ;
              originaltable.field3, newvalue)
ENDSCAN