You can use
xfconf-query to edit Appearance settings from command line.
Set Window Manager:
xfconf-query -c xfwm4 -p /general/theme -s Numix
xfconf-query -c xsettings -p /Net/ThemeName -s Numix
Set icon theme:
xfconf-query -c xsettings -p /Net/IconThemeName -s Numix
(I believe you need to install the Numix icon theme package in Xubuntu 14.04. It was not listed in mine.)
Set background image:
xfconf-query -c xfce4-desktop -p /backdrop/screen0/monitorHDMI-0/workspace0/last-image -s /path/to/your/image.jpg
In the man page for
The channel to query/modify
The property to query/modify
The new value to set for the property
If you remove the
-s and everything after it will tell you the current setting for what you are querying.
To make your own particular changes, you can open Settings Editor. Find the left hand menu item that contains the category that you want to change. This is the channel
-c. Then for the property
-p you can click on the property (for example, theme) to highlight it then click Edit to get the path. Finally type the name for what you want to change it to. It is caps sensitive. If there are two words, you'll want to put quotes around it. If there is an error in the name it goes to default. You'll need to add in the specifics of your display and background image.
The commands above change the following configuration files:
Enjoy! Sounds like a nice project. :)