I would like to developp my own tweak. It will use a shell script to replace some UI sounds.
There is my script:

chmod 755 /System/Library/Audio/UISounds

cd /System/Library/Audio/UISounds/tmp_*myapp*

cp Bubble.caf /System/Library/Audio/UISounds

cd /System/Library/Audio/UISounds

mv Tock.caf sauvegarde_Tock.caf
mv Bubble.caf Tock.caf

exit 0

When I try to run the script in Mobile Terminal, I got:
chmod: changing permissions of '/System/Library/Audio/UISounds': Operation not permitted

I've understood that I have to be the root user for run this command line but how I can to do ? I mean how can I write my script for "chmod" works on all iDevices that have downloaded my tweak ?!

I hope you will understood my goal, English is not my primary language ^^'
Thanks in advance for your help !