You can create a template for a wiki group by creating the special page "GroupTemplate". Once this page exists each new page in the group will have this template page as it's initial contents.

ChurchOnlyProfiles.Group Template is an example. See how it works by accessing the following page (''without' saving it!): ChurchOnlyProfiles.A Profile That Shoud Not Exist.

You can find more information on the Cookbook:PageTemplate page.