The IOPWC command is used for changing the password for login to an IPU board, there is no username. The cammand required to change a login on an NIU board is IOUAC:NAME=....,PSW......,AUTH=n; where n is 0 to 7.
The MDUSER login is auth 7, to change this Password, use the command as follows: IOUAC:NAME=MDUSER,PSW=.......;