I have installed the Ubuntu MATE Remix desktop environment on Ubuntu 15.04 (Please note I have a regular Ubuntu installation with the desktop environment on it, not the Ubuntu MATE flavor of Ubuntu). I use this as my main desktop environment. Will installing the vannila MATE desktop environment (to try it out) break my Ubuntu MATE Remix installation?
You can have multiple DE's at the same time, and you will be able to choose one of them when you boot Ubuntu. To do this, run the following commands in a terminal emulator (Ctrl+Alt+T):
sudo apt-add-repository ppa:ubuntu-mate-dev/ppa sudo apt-add-repository ppa:ubuntu-mate-dev/trusty-mate sudo apt-get update sudo apt-get upgrade sudo apt-get install --no-install-recommends ubuntu-mate-core ubuntu-mate-desktop
The "--no-install-recommends" attribute is very important in this process. It tells APT not to overwrite anything. After all this process ends, you can log out your current session and choose other DE at the login screen (above your user icon, near the hour applet).