Wikimedia Bugzilla is closed!

http://www.mediawiki.org/wiki/Manual:Preventing_access#Restrict_account_creation says
New users will still be able to be created by sysops, in the following manner:
   1. Go to [[Special:Userlogin]], when logged in as a sysop.
   2. Click on "Create an account" to get to the account creation form.
   3. Enter a username and an email address, and click the "by email" button.
   4. The account will be created with a random password which is then emailed to the given address.

But that won't work if $wgEnableEmail=false, there will be no such button.

One either has to open up their wiki to $wgEnableEmail=true and all
that it implies, or forget about being able to use the above steps.

$wgHooks['UserCreateForm'], $wgHooks['addNewAccount'] scope is not high
enough to remedy the situation either.

So at least the sysop can create new accounts, but he has no way via
the web interface of changing a password once forgotten -- he never
did (there was only the email 'send a new password facility'.)
Now he can only use changePassword.php via the shell.