Unfortunately, the Econet implementation in the original BBC Micro's had very little in the way of security.
The station ID was coded using a set of dip-switches under the top cover, on the keyboard PCB, but this was read into a location in page 0 of the RAM. As the 6502 and BBC OS did not have any concept of a privilege mode, it was possible to change the station ID with a simple command.
There was a vague idea of a privileged user when you logged into the file server (and there was some minimal user-seperation on the fileserver), but again, the User ID and whether they were privileged or not was stored in page 0 again, and could easily be changed.
It was the nature of the machines. There was no real way of securing what was effectively an open workstation.
When I administered an Econet Level 3 network, I very quickly established that there was nothing that could be secured on the network, and told the teaching staff to only store course records on floppy, never on the fileserver.
It was a shame really, because it was a rather nice system (with one or two drawbacks, like security and very slow byte-by-byte access to files using OSDCH and OSWRCH)