Sorry for the delay with this update
@JB1970 - after a lot of back and forth, Hik have explained that the ability to edit user permissions locally on the NVR was deliberately removed on the V4 firmware on all K-Series models...
They say that this is to simplify the interface / improve performance, and that as the web interface and iVMS-4200 are more popular, they didn't feel it was necessary to keep this feature on the local GUI.
I've said that it would still be nice to have the ability to manage the user permissions locally, as in many cases (for installers / integrators), it is the simplest way to configure the NVR.