Rename Datafile in Oracle Tablespace

 sqlplus:  ALTER TABLESPACE cust_ts OFFLINE;

linux> mv 'OLDFILE.DBF ' 'NEWFILE.DBF'

sqlplus:  ALTER TABLESPACE
   cust_ts
RENAME datafile     
   '/u01/app/oracle/mysid/oldname.dbf'
TO
   '/u01/app/oracle/mysid/newname.dbf';