yes, to add a column you query the dbf to a temp space with the added column, then copy the query results back to the original file location.
CAUTION!!! I did not look up the syntax on this one,
but this should get you started.
if your dbf is
firstname char 20
lastname char 30
your query could be
select firstname,lastname,fistname&' '&lastname into c:\mytemp\newfile from c:\mytemp\oldfile
run copy c:\mytemp\newfile c:\mytemp\oldfile
if it is to be it's up to me