As mentioned, a theme consists of a subdirecory in the themes directory of the site. Best practice is, to copy the distributed "default" theme to another subdirecotory. With a shell, you may do something like
mkdir ./themes/myT
cp -R ./themes/default/* ./themes/myT/
or use ftp, scp, what you prefer or have ...
Assign theme with Layout Admin
Sure, the content of "myT" is just the same as "default" and without any danger we may assign the "myT" theme to the site. That is to do with Controlpanel/Administration/Layout/Themes:
But regard, the theme assignment task has a short finite time loop: When you select the theme to the site, you have to confirm within some seconds; else the theme assignment retains unchanged.
In the exception to have two themes equal in content, there is no difference to see in the layout. In the normal case, a theme differs from the former one and is seen immediatly. That is the reason why the theme change is to confirm. It may be possible, a theme quickly runs a site in an optical desaster and only when you agree with the new design just shown, you may agree. But as mentioned, because we want to change a theme with the native base of the default one, we agree the new theme:
eZine
