How to change the location of an Oracle external table
In the case that the underlying file of an external table has changed on the operating system, or you have now a newer version of it with a different extension, I have just found that the table doesn't have to dropped and recreated with a different definition.
The clause ALTER TABLE ... LOCATION is available for external tables;
ALTER TABLE ext_table LOCATION (directory,'file');
ALTER TABLE EXT_REFERENCE LOCATION (DIR_REF:'INPUTMOSCOW.476');
The database release I used is Oracle 10.2.0.4