New answers tagged theme
First, install the User Themes Extension. Having done that, you can unpack your downloaded themes into ~/.themes (so that they end up in ~/.themes/ThemeName, with the directory gnome-shell under that). Then, they'll show up in Gnome Tweak Tool. (You may have to restart the shell, with ALT-F2, a single r in the command dialog, and <enter>.)
To answer your main question - the only way you can do this is if you take the theme from Luna and port it over manually. :/ However, to disable autochanging on Freya, go to dconf editor, then open org>pantheon>desktop>wingpaneland you should see auto-adjust-alpha ticked. Untick that and change background-alpha to be 0.
This is a window manager theme (Xfce window manager), as you can tell by the presence of only the xfwm4 folder inside the theme zip. You can access it in Settings Manager -> Window Manager -> Style As an alternative install location, if you are the only user in your system, create a .themes (mind the dot) folder inside your home directory and unzip your ...
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