open xterm
sudo gainroot
cp /usr/share/icons/hicolor/scalable/hildon/*nokia* /media/mmc1

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the above comands will copy following files

qgn_indi_about_nokia_logo.png
qgn_indi_nokia_770.png
qgn_indi_nokia_hands.jpg
qgn_indi_startup_nokia_logo.png

take these files to you computer.
Edit these files to what ever you want.
Then move back to mmc card.
copy these files to /usr/share/icons/hicolor/scalable/hildon

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I am not sure if this allowed, if this violates the warranty.