I assume you are referring to the MKS Domain users, that you are using? (this would not apply for LDAP/AD users).
im edituser can't be used to do this, as that command works at the IM (Workflow & Documents) level.
The command you are looking for, is:
That command, is used to edit users in the MKS Domain, and it will be in that scope, where the password attribute can be changed, edited.
For options and help, the Integrity man page help can offer more info: