I have Gnome Shell, Unity and Xubuntu on my computer and I would like to use compiz in Xubuntu. Whenever I put in "compiz --replace" it changes my window's theme from Greybird to Gnome's Ambiance. It doesn't seem like I can change it back in Xubuntu's settings menu, when I click on Window Manager, everything is blank. Any suggestions?
When you use "compiz --replace", you are replacing xfwm4 with compiz. That means the xfwm4 window manager is no longer running. Since greybird is part of xfwm4, it won't run either.
You can try just logging out and back in as another shell (Click the gear) to get back into the settings. As well I got the Compwiz manager when I was messing around with it.
sudo apt-get install compizconfig-settings-manager