Is there a partition utility in Ubuntu from which I can break my existing 'ext4' partition into more partition w/o loosing this partition's data?
You can with gparted it is part of ubuntu. Be sure to resize that partition first (shrink it) and freespace that left will be turned in unallocated space. Make new partition from that unallocated space. You can shrink it with graphic slider.
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you can use gparted which can be installed by typing into a terminal
"sudo apt-get install gparted" (without quotes)
and then by either pressing alt-f2 or in a terminal write "gksudo gparted" (without quotes)
gparted help is located here http://gparted.sourceforge.net/help.php
edit: read your modification to the question.
you have to unmount the partition to edit it. also you may use a live cd/usb to edit the partition, too. with same steps.