Sim, você certamente pode, mesmo que seja o seu DE original.
Para fazer isso, execute o seguinte comando muito longo:
sudo apt-get remove adium-theme-ubuntu aisleriot apg apport-gtk aptdaemon aptdaemon-data apturl at-spi2-core bamfdaemon banshee banshee-extension-soundmenu banshee-extension-ubuntuonemusicstore baobab binfmt-support bluez-gstreamer branding-ubuntu brasero brasero-cdrkit brasero-common checkbox checkbox-gtk cli-common compiz compiz-core compiz-gnome compiz-plugins-default compiz-plugins-main-default compizconfig-backend-gconf deja-dup desktop-file-utils dmz-cursor-theme doc-base duplicity empathy empathy-common eog espeak espeak-data evince evince-common evolution-data-server evolution-data-server-common example-content file-roller firefox firefox-globalmenu firefox-gnome-support gamin gbrainy gcalctool gcc gcc-4.6 gconf2 gconf2-common gedit gedit-common geoclue geoclue-ubuntu-geoip ginn gir1.2-appindicator3-0.1 gir1.2-atk-1.0 gir1.2-atspi-2.0 gir1.2-dbusmenu-glib-0.4 gir1.2-dbusmenu-gtk-0.4 gir1.2-dee-0.5 gir1.2-freedesktop gir1.2-gconf-2.0 gir1.2-gdkpixbuf-2.0 gir1.2-gmenu-3.0 gir1.2-gnomebluetooth-1.0 gir1.2-gtk-2.0 gir1.2-gtk-3.0 gir1.2-gtksource-3.0 gir1.2-indicate-0.6 gir1.2-launchpad-integration-3.0 gir1.2-notify-0.7 gir1.2-pango-1.0 gir1.2-peas-1.0 gir1.2-soup-2.4 gir1.2-totem-1.0 gir1.2-totem-plparser-1.0 gir1.2-unity-4.0 gir1.2-vte-2.90 gir1.2-webkit-3.0 gir1.2-wnck-3.0 gksu gnome-accessibility-themes gnome-bluetooth gnome-codec-install gnome-control-center gnome-control-center-data gnome-desktop-data gnome-desktop3-data gnome-disk-utility gnome-font-viewer gnome-games-common gnome-icon-theme gnome-icon-theme-symbolic gnome-keyring gnome-mahjongg gnome-media gnome-menus gnome-nettool gnome-online-accounts gnome-orca gnome-power-manager gnome-screensaver gnome-screenshot gnome-search-tool gnome-session gnome-session-bin gnome-session-canberra gnome-session-common gnome-settings-daemon gnome-sudoku gnome-system-log gnome-system-monitor gnome-terminal gnome-terminal-data gnome-user-guide gnome-user-share gnome-utils-common gnomine gstreamer0.10-gconf gstreamer0.10-nice gstreamer0.10-plugins-base-apps gstreamer0.10-tools gtk2-engines gtk2-engines-murrine gtk3-engines-unico gucharmap guile-1.8-libs gvfs gvfs-backends gvfs-bin gvfs-fuse gwibber gwibber-service gwibber-service-facebook gwibber-service-identica gwibber-service-twitter humanity-icon-theme hwdata ibus ibus-gtk3 ibus-pinyin ibus-pinyin-db-android ibus-pinyin-db-open-phrase ibus-table indicator-application indicator-appmenu indicator-datetime indicator-messages indicator-power indicator-session indicator-sound indicator-status-provider-mc5 intel-gpu-tools jockey-gtk language-selector-gnome launchpad-integration libappindicator0.1-cil libappindicator1 libappindicator3-1 libatk-adaptor libatkmm-1.6-1 libatspi2.0-0 libavahi-glib1 libavahi-gobject0 libavahi-ui-gtk3-0 libbamf0 libbamf3-0 libboost-serialization1.46.1 libbrasero-media3-1 libburn4 libc-dev-bin libc6-dev libcairo-perl libcairomm-1.0-1 libcamel-1.2-29 libcanberra-gtk-module libcanberra-gtk0 libcanberra-gtk3-0 libcanberra-gtk3-module libcap2-bin libcdio-cdda0 libcdio-paranoia0 libcdio10 libcompizconfig0 libcroco3 libdbus-glib1.0-cil libdbus1.0-cil libdconf-dbus-1-0 libdconf-qt0 libdconf0 libdecoration0 libdee-1.0-1 libdotconf1.0 libebackend-1.2-1 libebook1.2-12 libecal1.2-10 libedata-book-1.2-11 libedata-cal-1.2-13 libedataserver1.2-15 libedataserverui-3.0-1 libespeak1 libevent-2.0-5 libevince3-3 libexempi3 libfolks-telepathy25 libfolks25 libgail-3-0 libgail-3-common libgail-common libgail18 libgamin0 libgck-1-0 libgconf2-4 libgconf2.0-cil libgcr-3-1 libgd2-xpm libgdata-common libgdata1.7-cil libgdata13 libgdiplus libgdu-gtk0 libgdu0 libgee2 libgeoclue0 libgexiv2-0 libgkeyfile1.0-cil libgksu2-0 libglew1.5 libglewmx1.5 libglib-perl libglib2.0-bin libglib2.0-cil libglib2.0-data libglibmm-2.4-1c2a libgmime-2.4-2 libgmime2.4-cil libgnome-bluetooth8 libgnome-control-center1 libgnome-desktop-3-2 libgnome-media-profiles-3.0-0 libgnome-menu-3-0 libgnome-menu2 libgnome2-common libgnomekbd-common libgnomekbd7 libgnomevfs2-0 libgnomevfs2-common libgoa-1.0-0 libgomp1 libgpod-common libgpod4 libgrip0 libgssdp-1.0-2 libgstfarsight0.10-0 libgtk-3-0 libgtk-3-bin libgtk-3-common libgtk-sharp-beans-cil libgtk-vnc-2.0-0 libgtk2-perl libgtk2.0-cil libgtkmm-3.0-1 libgtksourceview-3.0-0 libgtksourceview-3.0-common libgtkspell0 libgtkspell3-0 libgtop2-7 libgtop2-common libgucharmap-2-90-7 libgudev1.0-cil libgupnp-1.0-3 libgupnp-igd-1.0-3 libgvnc-1.0-0 libgweather-3-0 libgweather-common libgwibber-gtk2 libgwibber2 libibus-1.0-0 libidl0 libido3-0.1-0 libindicate-gtk3 libindicator-messages-status-provider1 libindicator3-6 libindicator6 libisofs6 libjson-glib-1.0-0 libjte1 libkpathsea5 liblaunchpad-integration-3.0-1 liblaunchpad-integration-common liblaunchpad-integration1 liblaunchpad-integration1.0-cil liblightdm-gobject-1-0 liblircclient0 liblouis-data liblouis2 liblua5.1-0 libmetacity-private0 libminiupnpc5 libmission-control-plugins0 libmono-addins-gui0.2-cil libmono-addins0.2-cil libmono-cairo4.0-cil libmono-corlib4.0-cil libmono-csharp4.0-cil libmono-i18n-west4.0-cil libmono-i18n4.0-cil libmono-posix4.0-cil libmono-security4.0-cil libmono-sharpzip4.84-cil libmono-system-configuration4.0-cil libmono-system-core4.0-cil libmono-system-drawing4.0-cil libmono-system-security4.0-cil libmono-system-xml4.0-cil libmono-system4.0-cil libmono-zeroconf1.0-cil libnatpmp1 libnautilus-extension1 libnice10 libnm-gtk-common libnm-gtk0 libnotify-bin libnotify0.4-cil libnotify4 libnux-1.0-0 libnux-1.0-common liboauth0 libopencc1 liborbit2 liboverlay-scrollbar-0.2-0 liboverlay-scrollbar3-0.2-0 libp11-kit0 libpam-gnome-keyring libpango-perl libpangomm-1.4-1 libpeas-1.0-0 libpeas-common libpoppler-glib6 libportaudio2 libprotobuf7 libprotoc7 libpurple-bin libpurple0 libqtbamf1 libqtdee2 libqtgconf1 libquadmath0 libquvi0 librarian0 libreoffice-gnome libreoffice-gtk libreoffice-help-en-us libreoffice-style-human librest-0.7-0 librsvg2-2 librsvg2-common librsync1 libsdl1.2debian libsdl1.2debian-pulseaudio libsigc++-2.0-0c2a libstartup-notification0 libsyncdaemon-1.0-1 libt1-5 libtaglib2.0-cil libtelepathy-farsight0 libtelepathy-glib0 libtelepathy-logger2 libtotem-plparser17 libtotem0 libubuntuone-1.0-1 libubuntuone1.0-cil libunique-1.0-0 libunique-3.0-0 libunity-2d-private0 libunity-core-4.0-4 libunity-misc4 libunity6 libutouch-geis1 libuuid-perl libvte-2.90-9 libvte-common libvte9 libwebkitgtk-1.0-0 libwebkitgtk-1.0-common libwebkitgtk-3.0-0 libwebkitgtk-3.0-common libwmf0.2-7 libwmf0.2-7-gtk libwnck-3-0 libwnck-3-common libwnck-common libwnck22 libxklavier16 libxres1 libyaml-tiny-perl libyelp0 libzeitgeist-1.0-1 libzephyr4 light-themes lightdm linux-headers-3.0.0-12 linux-headers-3.0.0-12-generic linux-headers-generic linux-libc-dev make manpages-dev media-player-info metacity metacity-common mono-4.0-gac mono-gac mono-runtime mousetweaks nautilus nautilus-data nautilus-sendto nautilus-sendto-empathy nautilus-share network-manager-gnome network-manager-pptp-gnome notify-osd notify-osd-icons nux-tools onboard oneconf overlay-scrollbar pinyin-database pkg-config plymouth-theme-ubuntu-logo policykit-1-gnome protobuf-compiler pulseaudio-module-gconf python-appindicator python-aptdaemon python-aptdaemon-gtk python-aptdaemon.gtk3widgets python-aptdaemon.gtkwidgets python-brlapi python-configglue python-dateutil python-defer python-egenix-mxdatetime python-egenix-mxtools python-farsight python-gconf python-gnomekeyring python-gst0.10 python-gtk2 python-ibus python-indicate python-libproxy python-libxml2 python-louis python-notify python-openssl python-pam python-papyon python-piston-mini-client python-protobuf python-pyatspi2 python-pyinotify python-serial python-speechd python-support python-telepathy python-twisted-bin python-twisted-core python-twisted-names python-twisted-web python-ubuntuone-client python-ubuntuone-control-panel python-ubuntuone-storageprotocol python-virtkey python-vte python-webkit python-wnck qt-at-spi rarian-compat rdesktop seahorse sessioninstaller shotwell simple-scan sni-qt software-center software-properties-common software-properties-gtk speech-dispatcher ssh-askpass-gnome system-config-printer-gnome telepathy-butterfly telepathy-gabble telepathy-haze telepathy-idle telepathy-indicator telepathy-logger telepathy-mission-control-5 telepathy-salut thunderbird thunderbird-globalmenu thunderbird-gnome-support tomboy totem totem-common totem-mozilla totem-plugins transmission-common transmission-gtk ubufox ubuntu-artwork ubuntu-desktop ubuntu-docs ubuntu-mono ubuntu-sounds ubuntu-sso-client ubuntu-system-service ubuntu-wallpapers ubuntuone-client ubuntuone-client-gnome ubuntuone-control-panel ubuntuone-control-panel-gtk ubuntuone-couch ubuntuone-installer unity unity-2d unity-2d-launcher unity-2d-panel unity-2d-places unity-2d-spread unity-asset-pool unity-common unity-greeter unity-lens-applications unity-lens-files unity-lens-music unity-scope-musicstores unity-services update-manager update-notifier usb-creator-gtk vinagre vino whois xdg-user-dirs-gtk xdiagnose xul-ext-ubufox yelp yelp-xsl zeitgeist zeitgeist-core zeitgeist-datahub zeitgeist-extension-fts zenity zenity-common && sudo apt-get install kubuntu-desktop
Fonte: link
Nota: Remover apenas ubuntu-desktop não irá desinstalar todos os pacotes do Gnome.