Hello!
I just have added a line to the CommonSettings.php (and deleted the
individual lines at InitialseSettings.php) allowing each wiki to
block logged in users.
Please note that whilst this feature is technically available, this
doesn't mean you necessarily have the right to use it, because there
might be policies on your wiki restricting this.
You can block a logged in user like you would block an IP, typing in an
username instead of an IP.
Sincerly yours,
Fire