Currently we hardcode the settings for guest and superadmin (e.g. the default editor, whether the user is advanced or not, whether the user sees hidden docs, the display name, etc).
For example in https://jira.xwiki.org/browse/XWIKI-17104 I proposed to have the default editor for superadmin be the text editor because I thought that superadmin is a technical user who should have all the power and the text editor is the lowest denominator (the wysiwyg editor might not even exist in a given flavor). But I can imagine some users wanting that their superadmin user have the wysiwyg editor set by default.
So my proposal is to introduce config options in xwiki.properties for these special users:
user.superadmin.<property key>=<value> user.guest.<property key>=<value>