Hi,
Modifying the NAB design is not recommended at all. Instead of giving your people author access to these docs, I would advise using an external DB. Usually its best to let your users handle an reset their passwords if needed, this can be done with a single form that identifies the user (@Username) and an agent that has the proper rights to edit person docs in your NAB, and write the hashed password into the HTTPPassword field. This way you don't have to grant access to the documents, plus it's pretty simple to create some logs so your helpdesk people can keep track and or initiate these password changes.
By the way I've had to assign new HTTP passwords to all users in our NAB once, and found ytria's scanez tool extremely useful - it would let you make changes (like assign hashed values to the HTTPPassword items) without having to do any coding - cool stuff.
Cheers
Wade