Dave, thanks for your response. That gives a little more insight.
What would really help, is something like an example or some pointers how to edit/modify one of these menu drop-downs (or are it groups?) and replace the original one with it (as I understand that's how it should be done now), using the web-extensions folder.
As I'm not really sure where to look for the new files that are used by the new header, I hope you can help with that as well.
And also: it would be rally nice to be able to hide the Repository and Create Site links for non-admins, but show it for admins. Not completely remove them. I know what URL to use, but probably not all admins in the world do 😉
Also, in "tomcat/webapps/share/WEB-INF/classes/alfresco/site-webscripts/org/alfresco/modules/header/sites.get.html.ftl" I see things like <#if showCreateSite> and <#if showFindSites>. This is what I'd normally use to add an admin-only check. How/where can you configure these switches?