changing De or reinstalling ubuntu with different flavour

I would like to change my Ubuntu OS from Gnome 3 to Ubuntu Mate. I know I can install Mate DE and change back and forth. Can I remove the Gnome 3 DE and keep only the Mate DE. Also I have an attachment of my OS partition scheme and was wondering if I can install Mate on the root partition seeing as my home is on a separate partition. Any advise would help.
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