Changing the UI password in OH 3.0?

Setup, Configuration and Use Installation
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6

Ok, there is a jaas:role-add command. This then worked (in addition to the previous deletion and re-add of the user openhab):

openhab> jaas:realm-manage --index 6
openhab> jaas:role-add openhab administrator
openhab> jaas:user-list
User Name │ Group │ Role
──────────┼───────┼──────────────
openhab   │       │ administrator
openhab   │       │ user
openhab> jaas:role-delete openhab user
openhab> jaas:user-list
User Name │ Group │ Role
──────────┼───────┼──────────────
openhab   │       │ administrator
openhab   │       │ user
openhab> jaas:role-delete openhab user
openhab> jaas:user-list
User Name │ Group │ Role
──────────┼───────┼──────────────
openhab   │       │ administrator
openhab   │       │ user
openhab> jaas:update
openhab> jaas:user-list
No JAAS Realm/Login Module has been selected
                                            ~                                                                                openhab> jaas:realm-manage --index 6
openhab> jaas:user-list
User Name │ Group │ Role
──────────┼───────┼──────────────
openhab   │       │ administrator
openhab>

Edited to mention that the jaas:role-add command was mentioned in the thread I just checked out from @hafniumzinc. Good lead!