This  index  was  previously  specified  with  a  STORE  clause,
  continue?  [N]

  Explanation:   You  are  specifying  a  CHANGE  INDEX  statement
  without  a  STORE  clause,  which  places  the  index  into  the
  RDB$SYSTEM storage area.  The index was previously specified  as
  being  stored  in  a different area.  RDO is confirming that you
  want the index placed in the RDB$SYSTEM storage area.

  User Action:   An  affirmative  reply  (Y  or  YES)  causes  the
  operation  to continue.  A negative reply (a carriage return, N,
  or NO) terminates the operation.