If you want to make that big a mess, you will have to download and install your own copy. Go on, it's not that hard.
I actually have a copy of Moodle 2.0 from CVS on my development machine (for heavy messing), but for quickly checking things it's easier to just use the official QA site
But seriously, shouldn't at least some of the admin features (especially the new themes) be available for testing for everyone? It would also make comparing the new "Manager" role with the "Administrator" role easier. Some people might falsely assume that "Manager" is only a renamed "Administrator".
After all, any mess one could create would at most last one hour...
And http://demo.moodle.net has always provided admin access.
But the comparable harmless feature of changing the theme for a course is restricted to Site Admins. Shouldn't there be some kind of Course Admin for all the technical stuff related to a course?
"Manager role is supposed to replace original 'small administrators' that were assigned at a course category level."
Development:Role archetypes#New Manager role
I suppose I better read Development:Roles administration improvements for Moodle 2.0 first and then post to the Roles and Capabilities forum
Frank, as you mention http://demo.moodle.net/ provides a demo account, however http://qa.moodle.net/ is really for testing and not just for trying out the features in Moodle 2.0. If there are several people logged in as an admin at the same time, all making admin setting changes, then it becomes difficult to test things.
If anyone in our testers group would like admin access to the QA testing site in order to test admin features, please contact me to request an admin login.