In response to a Forum post I wrote some quick SQL to allow you to update the default Portal Skin to the standard MinimalExtropy skin that comes with DNN. You need to run this as SQL on your database, and make sure you change the PortalId to match the appropriate portal and add your objectQualifier, if used.
Original Forum ThreadYOU SHOULD ALWAYS BACKUP YOUR DATABASE BEFORE RUNNING SQL SCRIPTS
update portalsettings
set SettingValue = '[G]skins/MinimalExtropy/index.ascx'
where SettingName = 'DefaultPortalSkin'
and PortalId=0