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The CSC code contains the info about software packages specific to a particular region, carrier branding and also APN settings for data connection. In this way, unless the PDA, PHONE and CSC codes do not match correctly, you will not be able to update your device over Samsung Kies or via OTA"

Thats why you see "Your device does not support software upgrading via kies" message every time you open Kies software
Instructions :
Backup your data first because changing CSC will wipe all your data
1 -Download "Samsung Galaxy S / S2 / S3 CSC" app (Link below)
2 -Open the app
If your device on "XXELLA" or later ,Select "Try with ROOT mode"
3 -Press "Change CSC"
4 -Select the CSC that you want ...
5 -Press "INSTALL"
-Your device will automatically reboot by itself
Notes :
~ This app work only on official Samsung FW for the galaxy S/Note/Tab Phones/Tablets devices! Custom ROM not supported
~ You can change CSC if your current FW is Multi CSC packages
~ If your device has been updated to "XXELLA" or later
your device must be rooted first (void the warranty) for you become able to change the "CSC"

Links :
"Samsung Galaxy S / S2 / S3 CSC" app http://tiny.cc/iyoMrW
CSC regoin code list http://tiny.cc/3obMrW