This password file format is compatible with Level 3, FileStore and awServer. There are various tools available for editing these "Passwords" files, but I (obviously) recommend my !BudgieMgr (which can also import/export in a variety of formats).
Each user in the password file format has 31 bytes to describe them. The file must be padded out to a whole sector (file size must be a multiple of 256 bytes) so the only clear way to count the number of users is to step through the file and see.
0 - 19 Twenty bytes for username, null terminated if less than
twenty characters. A null username indicates that the
user has been deleted.
20 - 25 Six bytes for password, null terminated if less than six
characters.
26 - 29 A word (four bytes) for user freespace.
30 Boot option (lower four bits) and privilege
(upper four bits).
The user name is the URD.