$ cat > somestuff.csv
10004,Able,Baker,able.baker@notrealemail.com
14634,Charley,Delta,charley.delta@notrealemail.com
12886,Echo,Foxtrot,echo.foxtrot@notrealemail.com
14366,Golf,Hotel,golf.hotel@notrealemail.com
10178,India,Juliet,india.juliet@notrealemail.com
10164,Kilo,Lima,kilo.lima@notrealemail.com
10124,Mike,November,mike.november@notrealemail.com
$ perl -pi -e 's/\Z/,UF,A,Y,9,U/' somestuff.csv
$ cat somestuff.csv
10004,Able,Baker,able.baker@notrealemail.com,UF,A,Y,9,U
14634,Charley,Delta,charley.delta@notrealemail.com,UF,A,Y,9,U
12886,Echo,Foxtrot,echo.foxtrot@notrealemail.com,UF,A,Y,9,U
14366,Golf,Hotel,golf.hotel@notrealemail.com,UF,A,Y,9,U
10178,India,Juliet,india.juliet@notrealemail.com,UF,A,Y,9,U
10164,Kilo,Lima,kilo.lima@notrealemail.com,UF,A,Y,9,U
10124,Mike,November,mike.november@notrealemail.com,UF,A,Y,9,U
$