[Mediawiki-l] How to change the Permission error page for users who aren't permitted to edit

[The Gadget Doctor]

I have a private wiki of which the majority of users are viewers only
(not logged in, no editing rights).

When they follow a link to a wanted page or category I'd like to show
them a note saying the name of the page and giving a brief message
about why it hasn't been built yet.

Instead all they see is Permission Error and some fairly terse text
about why they can't see anything.

Is there a way to change this behavior?

GD