I'm trying to upload a new or edit the default web page template on my Sharepoint external site but can't see how to do it either through the UI or Sharepoint designer. All my googling is bring back results for working with internal team sites, not customer facing sites, which seem to behave very differently.
How are you supposed to work with templates on these sites?
UPDATE: I found the master page being used but when I edit it (even just adding a line break) I get message saying:
"Saving your changes will customize this page so that it is no longer based on the site definition. Do you want to continue?"
Selecting 'no' discards my changes, selecting 'yes' saves but if I reload the site I get an error:
"The base type 'Microsoft.SharePoint.Spx.WebsiteCore.RootMaster' is not allowed for this page. The type is not registered as safe."